"An error occurred while fetching folder content."

As per this comment here, I've created a new issue, although the high-level problem description is similar to what's happening here

I am on Ubuntu 18 with Firefox 77.0.1 (64-bit) and this is happening to me on a private GitLab project. In fact, at the moment, it appears to be happening to all projects within our group. I didn't see any obvious errors in the Network inspection - I saw 200s and 304s. I did see, however, that there was no response for a couple of GraphQL requests that looked to be trying to grab maybe the latest commit for the repo ...

Please help! Major blocker here. Thanks.