This site has been up and running for the last couple of years without issue. Today we noticed we couldn't access the entries on the only Form that is set up. No obvious errors in Trace although it might be timing out on "umbraco/backoffice/UmbracoApi/Authentication/GetRemainingTimeoutSeconds".

Then noticed that when you click the user icon in the top left where you usually see the version etc, it just has template placeholder code like "link your {{login.caption}} account" and {{property.caption}}.

When you go into the Users section there isn't the usual list of users and green "invite user" button, it seems to be going straight to the Invite user screen but again, there are placeholders and other nonsense going on. Console has "DependencyHandler.axd?s=L3VtYnJhY28vbGliLIuanM7&t=Javascript&cdv=20201124:8 Error: Unknown provider: umbWordLimitFilterProvider <- umbWordLimitFilter"

So I'm wondering if the Form/Entries issue is an authentication issue - there seems to be something going on with the Users throughout.

We have a test site running in parallel, it is the same vintage and is running fine at the moment. No packages installed except Forms. Any ideas where to start? I have restarted the App pool and that didn't help. Thanks!!