I’ve had intermittent issues with T-Mobile on hotspot too. I’m not sure how helpful this will be but here’s my 2 cents. The only params I played with that seemed to help were the :
1- MTU (if I remember correctly, I had to dial it down to 1300)
2- and using IPv6 instead of v4.
This will depend on the APN you’re using for T-Mobile. I believe they have a legacy one that only uses IPv4 whereas their new one supports IPv6 only (I wasn’t able to find clear info about this but this is my guess). In any case, I have my wireguard server setup to support and use both IP versions and when v4 doesn’t work for me, switching to v6 fixes the issue for a while. At some point I even suspected they were heavily throttling wireguard traffic, which may be the case but who knows.
I hope this helps, good luck!
Many good suggestions on here. I have Rockstor running on mine. When I built my NAS, it was the only OS that used BTRFS for the FS (and I really like BTRFS) so I went with it.
Edit: also I have it running in Proxmox as a VM.