Originally Posted by David M
I had a similar problem with some of my Fotodiox OM to 4/3 adapters. I had to depress the lens release to get the lens to rotate enough and lock.
Ditto on one of my adapters. But I cannot see why even under close inspection of the mount, rotation stop pin or the elongated locking hole.
I do have a tiny mark on one that looks like the locking hole may not be quite deep enough and the pin hits the bottom of the hole on locking.
If I was investigating I'd look first at the depth of the elongated locking hole.