BTRFS is killing my NAS

I'm running 6.8.1. I never enabled quota but reading forums it seems like it might have been enabled automatically by a certain firmware update. As part of the troubleshooting (and desperation), I pulled the plug and was able to log in via SSH, which was responsive despite btrfs-transacti process starting to eat up CPU. I had pulled the plug before - the system usually worked for a few minutes before stalling again. So this time I immediately issued this:

btrfs quota disable /data

It's been 15 minutes so far and I don't see any btrfs activity - all services are available.

Now that I can actually access the system, I looked at the GUI logs. The last entry is from snapshot prune worker from 11/2 23:19, the next message is from today when I restarted it. Logs in journalctl indicate there was an out of memory condition around that same time.

Here the output of some btrfs commands.

btrfs fi df /data
Data, single: total=3.84TiB, used=3.47TiB
System, DUP: total=32.00MiB, used=672.00KiB
Metadata, DUP: total=3.00GiB, used=1.74GiB
GlobalReserve, single: total=485.88MiB, used=2.91MiB
root@NAS:~# btrfs fi show
Label: '0e35c581:data'  uuid: 07dfdef1-b26e-474a-b2ca-42a55738cb01
        Total devices 1 FS bytes used 3.47TiB
        devid    1 size 4.54TiB used 3.85TiB path /dev/md127
root@NAS:~# df -h /data
Filesystem      Size  Used Avail Use% Mounted on
/dev/md127      4.6T  3.5T  1.1T  76% /data

What is the best approach now to do any necessary btrfs maintenance? I had a monthly defrag which I disabled for now. I'm afraid to run balance as I had bad experience with it in the past (system locks up).