u/OneInchPunchMan

Hey r/linuxadmin , I have a weird one.
I have a NAS and a Server where the NAS serves /mnt/storage via NFSv4 to the Server.
There is also a user gitea:gitea (5203:5203) on both the NAS and Server admin is part of the gitea group.
The dir structure is:
/mnt/storage/ (775 admin:admin)
/mnt/storage/a.txt (775 gitea:gitea)
/mnt/storage/gitea/ (775 gitea:gitea + setgid)

My problem is that both admins can rw the a.txt file fine (appear to be in group gitea), however they cannot make new files in gitea/ dir (appear to be in "others").
How and why is that and am I missing some key concept here?