Okay, while writing I actually found the error which is really strange, I will leave my original post here so I hope it helps other people or preventing the issue from happening again, not sure if it was something on my end but as I wrote it was doing the update, then nothing.
I copied over my profile config in the new install so I don't have to login again and can switch to CE quick. As I wrote below that caused the error again. After looking into the config I deleted the
LastVersionPermissionsFailed = b20150414.2 (or rather just the version number). After that Osu started perfectly fine, even updated and all fine now. I'm not sure why that line causes such a hard error, creating "dead processes" but I hope it will help.
Original Post.
I'm having some extremely weird error.
Since one update on Cutting Edge Osu! doesn't start at all.
That update seems to have went successful, but Osu! just didn't start.
It only created a dead process which refuses to be killed.
Fun fact, those don't even show up in the Windows10 Task Manager, not under details or processes.
A "taskkill /f /im osu!.exe" says that it successfully closed the processes but they remain in the process explorer. (using the PID directly doesn't help either)
The osu!.exe can't be deleted while those are active too.
Only a restart will get rid of them.
I tried installing Osu! again in another directory and run it there, working fine with Stable/Fallback branch.
Switching back to Cutting Edge will cause the same error.