Since you're on B2, you may want to go through each update on their GIT repo and see if there was a fix already for this issue. If there is, and you don't want to perform a full backup of your site for a (just in case) scenario, you can backup the file(s) that were changed by the fix and fix the error yourself (assuming there was one).

Though with this being a beta version of the application, and an outdated one at that, bug fixing at this point might be a bit hard for the devs, having to go back a few revisions to bug hunt.

All that said, other than assuming this is a UNA software related issue, has anything changed/updated on the server itself? Have you made any altercations to site injections from Studio? Recently change any PHP/Apache/NGINX config files?