I'm new to OMV, and just happened across a possible bug (I didn't test if it is repeatable).
I have 3 blank disks, which I was attempting to create filesystems on (EXT4). I picked the 1st disk, /dev/sdb1 and starting the creation process, and rather than wait a long period of time for it to finish I closed the dialog box (The option ' Close' is there ;p). I then attempted to create a FS on the next disk, which it appeared as if it would do without any errors or feedback. After closing out that dialog box nothing was added to the list of file systems (the 1st disk was still doing it's thing w/ a status of Initializing). So I tried to do the 3rd disk, and that's when everything seemed to completely break - The OMV UI interface kept popping up with communication errors.
Another thing to note, after closing the dialog box (while the FS is being created), and selecting 'Create' the UI will still present the same disk that's currently in use by the file creation process. After this process is completed, it gets removed from the list of disks to create filesystems on.
I forcefully powered down the system, and started over - this time waiting for each disks FS creation to be completed before proceeding to the next disk.
edit: it seems either my install is corrupted, or it's very easy to break the whole UI. I was changing the location where dockers home is, and then it ran into all kinds of errors. So I decided to start with a clean slate and remove docker. Did that, but it still showed in the UI. Rebooted, same thing. So then I removed OMV-Extras, and the same thing happened to it. It shows on the left side of the UI, but says RPC service 'OmvExtras's not found. But now it won't even let me add it back - doesn't show in the plugin list. At this point I'm going to have to start over, or move on.