Hi Hicsy,
I have nothing to do with that bug-tracker bot, I just like to follow the reproduction steps to see if any extra info/clarification is needed. (I blame years spent working in Quality Assurance for this impulse 
)
In this case, I was able to verify the bug, but called the poster out on imprecise language, The ClassDesigner is not “gone”, it’s still there, but the visual representation/mesh turns invisible. I just re-verified and it’s still happening. (Able to reproduce this just by loading a different level and then loading back in)
The bug-reporting processes were not as robust in the spring of 2024 as they are now, so just bumping this thread could get bug-tracker to notice. If you don’t see any acknowledgement in a week I’d try creating a new issue for this.