So find the User's HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList registry key (-1000)
Make sure that "ProfileImagePath" for User is set to C:\Users\User
It does. So nothing to change i guess.

If you don't need User_2 anymore, maybe you should just delete it. It is just causing more confusion.
I would gladly do that. However, can you tell me if there is a place where a "default installation path" exists? I am afraid that if i remove that user, the system will still try to reach it, somehow, if that "installation path" is something that does exist.

If by default, it reverts to the only user, being User, then, all SHOULD be good, right?