u/Financial_Cancel_376

I'm using Arduino IDE "Upload Using Programmer" to flash my ATtiny1624 PCBs with an Adafruit HV UPDI Friend. But it only works about ~30% of the time and only on certain computers. My desktop works, but not my mac running windows. This happens with both my custom PCBs and a bare ATtiny1624 MCU on a breakout board. Any tips?

When it fails, the board is recognized but then crashes:

pymcuprog.serialupdi.physical - INFO - Switching to '57600' baud
pymcuprog.serialupdi.application - INFO - SIB: 'tinyAVR P:0D:1-3M2 (04.59B0D.0)'
pymcuprog.serialupdi.application - INFO - Device family ID: 'tinyAVR'
pymcuprog.serialupdi.application - INFO - NVM interface: 'P:0'
pymcuprog.serialupdi.application - INFO - Debug interface: 'D:1'
pymcuprog.serialupdi.application - INFO - PDI oscillator: '3M2'
pymcuprog.serialupdi.application - INFO - Extra info: '(04.59B0D.0)'
pymcuprog.serialupdi.application - INFO - Using 16-bit UPDI
pymcuprog.serialupdi.link - INFO - LDCS from 0x00
Traceback (most recent call last):
  File "C:\Users\Ben\AppData\Local\Arduino15\packages\megaTinyCore\hardware\megaavr\2.6.11/tools/prog.py", line 289, in &lt;module&gt;
pymcuprog.serialupdi.physical - INFO - Closing port 'COM24'
...
pymcuprog.pymcuprog_errors.PymcuprogError: Unexpected number of bytes in response: 0 byte(s) expected 1 byte(s)

How to consistently flash ATtiny1624 board with UPDI Friend?