Thanks @unguul! I think my original issue managed to resolve itself somehow, maybe by the old snapshots being removed by schedule.
Amusingly though, while trying to resolve my most recent problem, a google search caused me to stumble on my own post and your answer, which turned out to be the key to helping me resolve it!
So for anyone else stumbling on this, here are a few more breadcrumbs that might help.
I had an issue where an NFS export would not start up after a reboot. There was a low level in the rockstor logs saying the NFS export couldn’t be created to to a failed mkdir command.
Error running a command. cmd = /usr/bin/mkdir -p /export/nextcloud/.daily_202406050230. rc = 1. stdout = [\'\']. stderr = [\'/usr/bin/mkdir: cannot create directory ‘/export/nextcloud/.daily_202406050230’: Operation not permitted\', \'\']\n']).
Turns out NFS does not get along with visible shares, as described here:
Unfortunately, the solution there didn’t work for me, as I could not delete the snapshots, I think because they were being exported via NFS. This post lead me to see where I could find that. A lot of going in seeming circles and using chattr -i /export/share/offending_snapshot followed by rm -r /export/share/offending_snapshot eventually got things cleared out, and I was able to delete snapshots. Then I was eventually able to re-make the NFS share, and things started working again.