New bug in NFS? Almost nothing playing from my NFS share, started like four days ago

1 You seem to have a deprecated NFS package still installed, armv7-libnfs-osmc, that might be causing a conflict with the Debian package, libnfs12. I don’t think any harm will occur if you remove the deprecated package:

sudo apt-get remove armv7-libnfs-osmc

then reboot.

2 Your log is showing an error message:

2021-01-30 22:39:21.390 T:3939885280 ERROR: Failed to close(mnt/Multimedia/Movies/The Big Short (2015)/The.Big.Short.2015.HDRip.XviD.AC3-EVO.srt) - close call failed with "NFS: Commit failed with NFS3ERR_ROFS(-30)"

that appeared recently here. The takeaway from that thread was that the OP should wait until after Kodi 19 is released and report back if it still occurs.