I had Freenas 11.3, and then when stable release of TrueNAS 12.0 was available to upgrade, upgraded. Shortly after, I got a problem with Get Plugins failed. I reinstalled freshly Truenas from scratch, rebuilt my pools, and now again I get the seemingly identical problem. See screenshot for more info.
Last thing I did before getting this error message was an attempt to mount a virtual machine. I installed one, tried and deleted it. Last time (initial install) I wasn't doing anything virtual machines, but I think I did delete a jail shortly before noticing the problem. Tring to give as much info to help.