I've had the same experience in the past. And going to the user profile in the original instance was also giving problems which makes it weird to say the least.

I could block it through a different way because opening a post made by it, you can see in the sidebar of the desktop site a summary of actions for the profile, and one of them is the block button.

ow this is really bad.

We might found it.. we seems to load all posts into memory.. stupid of course: https://github.com/MbinOrg/mbin/blob/58910f41f11cb969479692965182efbd8796a2a6/src/Repository/UserRepository.php#L120C24-L120C43