Olympus OM-2N mirror lockup.

Good day. As the title says, I have a camera with a mirror that jams at fast shutter speeds (usually 125 and faster), see at pic.1. The batteries are new. If you hold the mirror up with your finger while pressing the button, the mirror lever returns to its original position (along with the shutter), pic 2. Any advices?

is the mirror foam too thick that sometimes the mirror has a hard time going all the way up?

No, foam is thin and seems to be normal.