Hi everyone,

I’m having a strange issue with my CalDigit TS5 Plus setup on a new MacBook Pro 16-inch with M5 Max.

Every ~10 minutes, my monitor briefly goes black for about a second, and at the exact same time my Universal Audio Apollo x8 disconnects/reconnects (audio drops in Cubase).

What’s strange is that my external SSDs stay mounted and connected during this. So it doesn’t seem like the entire dock fully resets.

Devices connected to the TS5 Plus:

• Apollo x8
• 2x Samsung T7 4TB
• 1x Samsung T7 1TB
• 1x Samsung T5 1TB
• Native Instruments Komplete Kontrol S88 MK2
• Moog Sub37
• Arturia Akai MPK Mini IV
• SSL UF8+UF1 daisy chained
• Genelec GLM
• Monitor connected via DisplayPort

Computer:

• MacBook Pro 16” M5 Max

Nothing is connected to it except TS5 Plus.

Important detail:
With my previous MacBook Pro 16-inch with M1 Max, I did NOT have this issue.

The only issue I had on the M1 Max setup was that sometimes after restart, the SSDs would not appear until shutting down TS5 plus and turning on. But I never had display + Apollo disconnects like this.

I’m wondering if this could be:

• a TS5 Plus firmware issue
• M5 Max Thunderbolt compatibility issue
• thermal issue
• bandwidth/power delivery issue
• or something related to UAD/Apollo

Has anyone experienced similar behavior with TS5 Plus + Apple Silicon + audio setups? Especially where SSDs remain connected, but display/audio briefly disconnect together?

Hello, is it something you generally advise to do ? do you advise the ts5 over the ts4 to connect the new Studio Display ? any cons to do that ?

computer is MacBook Pro m4
thank you

I've spent about 8 hours troubleshooting why the new TS5 isn't connecting properly to neither my Thinkpad T14s nor my M1 MacBook Pro. It's inconsistent in how it connects to the Mac, and doesn't connect as Thunderbolt at all on the Thinkpad. I ordered a new Thunderbolt 5 cable (Cable Matters), tried all the firmware and registry updates I've found on this sub and others online, and it's still not working.

The TS5 Plus shows sold out now on Amazon, so I can't even reorder it unless I'm willing to wait 3-4 weeks (which I'm not). I'm going to try the Anker Prime Thunderbolt 5 dock, even though I don't like the port configuration nearly as much, but I need a dock ASAP. Really disappointed, but it seems like a common issue with this particular model.

I'm getting 100mbps tops with it, and I'm trying everything, but it keeps happening over and over again.

What should I do, and are you guys experiencing the same issue as I am?

Is there a tool or dashboard to view the status of all ports/speeds? It's not always clear to me what's happening in the Hub and what speed different devices are getting etc.

I connected my ts5plus to a TESmart KVM (DKS402-M24) overall it works really well but every once and a while I get some display artifacts etc. It'd be good to just view all the port status etc.

The cable provided isn't recognizing my macbook. The cable is not even charging my mac.
I'm using other cables for the meanwhile, they're charging but not recognizing it as a docking station.
Please help what to do except buying that overpriced cable from CalDigit? Any workaround?

I'm setting up my home office after retiring from a county Communications Director position. I used a CalDigit TS3 at work and ran two monitors off of it. I do a lot of video editing work, so I really would like to use two monitors.

In my home office, I am running a large 40" monitor through the CalDigit TS4 (DisplayPort connection). But when I try to connect a smaller second monitor via USB-C, it will not connect and is not recognized. The monitor will briefly power up and then display “No Signal”.

I have tried different ports on the rear of the TS4, swapped multiple TB4-rated cables (currently using a CalDigit TB4 cable), and cycled the CalDigit TS4.

If I connect the second monitor directly to my MacBook Pro (M2 Max), it shows right up and connects normally. However, I'd need to use the MacBook's ports for drives, not the monitor.

Does anyone have a similar experience and advice for me? Thanks in advance.

Hardware:

• MacBook Pro M4 Pro
• CalDigit TS5 Thunderbolt 5 Dock
• LG 27UP850K (4K 60Hz, USB-C with DP Alt Mode)
• BenQ EX271U (4K 165Hz, USB-C with DP Alt Mode)
• Both monitors connected via USB-C to the TS5 downstream Thunderbolt 5 ports
• macOS Tahoe 26.4.1

The Problem

When plugging the CalDigit TS5 dock into the MacBook, only the BenQ EX271U comes on. The LG 27UP850K gets no signal and does not appear in System Settings > Displays at all.

The only workaround that consistently works is plugging the LG in first before connecting the dock, or connecting the LG before the BenQ on every hot-plug event.

This happens whether the monitors are both going through the TS5, or the LG is plugged directly into one of the MacBook's built-in Thunderbolt 5 ports. The plug order requirement follows the LG everywhere.

What Was Tested and Ruled Out

• Dock port position - Swapping which TB5 downstream port each monitor uses made no difference. BenQ wins the enumeration race regardless of physical port.
• Bandwidth - Dropped BenQ refresh rate to 60Hz. No change.
• BenQ USB-C lane config - The BenQ EX271U has an OSD setting called "USB-C Config: USB 2.0 / USB 3.1 Gen1." USB 3.1 Gen1 splits the 4 USB-C lanes 2 for video and 2 for USB data, cutting video bandwidth in half. Switched to USB 2.0 (all 4 lanes for video). No change.
• Direct MacBook connection - Plugging the LG directly into the MacBook's built-in TB5 port instead of through the dock made no difference. Same plug order requirement.
• Deleting the WindowServer plist - Found the file at ~/Library/Preferences/ByHost/com.apple.windowserver.displays.[UUID].plist, moved it out, rebooted with both monitors connected. Both monitors came up correctly on boot. However, unplugging and replugging the dock immediately reproduced the issue. macOS rewrites the plist with BenQ as display 1 on the first hot-plug event.
• Cables - Worth noting that macOS Tahoe has become significantly stricter about cable signal integrity compared to Sequoia. Cables that shipped in monitor boxes are often not rated for the bandwidth required.

Root Cause

This is a race condition at the kernel-level Thunderbolt display tunnel allocation layer, made worse by macOS Tahoe.

Here is what happens when the dock cable is plugged in:

1. The kernel detects the Thunderbolt connection
2. The Thunderbolt controller enumerates all connected devices and allocates display tunnels
3. WindowServer asks the kernel what displays are available
4. macOS allocates display tunnels in first-come-first-served order

The BenQ EX271U is a gaming monitor with firmware optimized to respond to EDID queries as fast as possible to minimize input lag. The LG 27UP850K is a productivity monitor with no such priority. The BenQ wins the EDID handshake every single time, claims the only available display tunnel before the LG can respond, and WindowServer never sees the LG.

macOS does not support DisplayPort MST (Multi-Stream Transport). On Windows, a dock can multiplex multiple display signals and the OS handles splitting them. macOS requires each monitor to have its own dedicated Thunderbolt display tunnel. On the M4 Pro, two display tunnels are available over a single Thunderbolt connection, but they must each be claimed independently during enumeration. If one monitor is too slow to respond, it simply does not get a tunnel allocated.

macOS Tahoe tightened the enumeration window compared to Sequoia. This was done to improve signal integrity by reducing tolerance for packet loss during handshake. The side effect is that the race condition is now much harder to win for a slower-responding monitor.

Why the Plist Fix Only Works on Boot

When the Mac boots with both monitors already connected and powered on, the Thunderbolt enumeration happens during kernel initialization before WindowServer starts. Both monitors get time to respond because there is no race, and both tunnels get allocated correctly. WindowServer then writes a fresh plist with both displays registered.

On a hot-plug event (unplugging and replugging the dock), the enumeration happens in real time with WindowServer already running and making immediate tunnel requests. The BenQ responds faster, claims tunnel 1, WindowServer immediately locks in that config, and the LG's slower EDID response arrives too late.

Current Status

This appears to be a known macOS Tahoe regression affecting M4 Pro users with dual monitors through Thunderbolt docks. Multiple threads on Apple Community forums report similar behavior after upgrading from Sequoia, including setups that worked perfectly before with no hardware changes.

The plug order workaround (LG first, then dock) works 100% of the time but is annoying for a daily desk setup.

Workarounds

Plug order - Always plug the LG in before connecting the dock cable. Takes about 5 seconds but is reliable.

Boot with both connected - If you leave your monitors connected and just sleep/wake the MacBook without unplugging the dock, both monitors come back correctly. The issue only occurs on full dock disconnect/reconnect.

Questions for the Community

• Has anyone found a way to add a delay to the Thunderbolt enumeration or force a display re-scan on dock connection via a script or launch agent?
• Has anyone seen this fixed in a specific Tahoe point release?
• Does anyone know if there is an EDID emulator or similar hardware solution that could slow down the BenQ's handshake response to level the playing field?

Tested on: MacBook Pro M4 Pro / CalDigit TS5 / macOS Tahoe 26.4.1