I’m having the same issue. Some assets from Fab will not download into my projects.
I’m currently on UE5.4 and all of the assets I use are meant to work on UE5.4. Yet I keep having this issue. On further investigation, I have noticed that every time a download fails, I get this response on my output log.
LogFab: Error: Invalid Manifest
I haven’t found a solution that fixes the issue yet.