This is a super old version of Rockstor. 3.9.1-0 was released 3 years ago. You could try for an update on either channel to see if it resolves this issue. But our CentOS based testing channel will only move you around 4 month newer. But our CentOS stable channel ended at 3.9.2-57 April this year 2020:
There is also a new ‘Built on openSUSE’ testing channel based on a server install of Leap 15.2:
Which was last release around 2 weeks ago as 3.9.2-60 and is nearing our next stable release:
You may well have an underlying problem, rather than a bug here, but the newer Rockstor versions, specifically the CentOS based Stable channel or the now newer ‘Built on openSUSE’ testing channel versions will be far more able to help you in that regard than this now very old version. Or it may be that your system drive has become corrupt/failing. But an update attempt or re-install may help to bring such issues to light anyway.
It would also help forum folk for your to provide a rough outline of your systems setup with regard to attached disks and the like. One command that may help here is:
btrfs fi show
So pasting the output of this command here may also guide others to chipping in with suggestions to narrow down what’s happened here. To me it looks like the indicated api paths are a little strange, unless you have a share called “2.Documents” but then this entire path was changed a couple of years ago in the code so again a newer code version would be advised.