I’m having almost the same issue.
When I try to drag something into the editor window or click “Add to project”, “Downloading” appears briefly and then nothing.
The console shows:
LogFab: Error: Failed to download FAB Asset Fence
(for a simple Fence asset from FAB)
Interestingly this only happens for one project, not for others. But this is a simple .fbx asset, no virtual texturing, so no idea what could be wrong in the project.