Unable to open termbases in Multiterm 2021 or add them to a project in Studio 2021

I installed SDL Studio 2021 (and Multiterm) as an upgrade from 2019 and updated the software. However, I have been unable to add a termbase in Studio, as I get an "OutOfMemoryException exception" or "already has an XML declaration node" message. If I try opening a termbase in Multiterm, I get a “cannot connect to the Multiterm server” message. The termbases I am trying to add are not excessively large.

I’ve lost a lot of time trying to resolve this following several KBs and advice from you (renaming settings and database files, uninstalling both apps and reinstalling them, even used SDL Freshstart), but still no luck. I am very disappointed with the performance (or lack) of the 2021 version.

Please help!