Leitz adapter not working on M6 - Please HELP

[Krosya]

Hello everyone,

Well, I came across something rather interesting. I have 2 LTM to M lens adapters (makes screw mount lenses fit M cameras). Both are made by Leitz. One is 5cm one and the other is 13.5cm. Both work correct on my M3 - means fit well, RF coupleing is correct and correct frame lines are brought up as each adpater fitted on the camera.
HOWEVER, while 5cm one works as it should on M6, the other one 13.5cm doesn't even want to fit it - I mean it doesn't turn far enough to lock in. Am I doing something wrong here? Or is there ajustment that I need to make to it? It is supposed to bring out 135/35 frames, which I have (mine is x.72), so it's supposed to fit. It's supposed to fit even if "wrong" or no frame lines would be brought up. But it doesn't want to. I'd think its a faulty adapter ring, but it works just fine on M3. Are the mounts THAT different on M6 and M3 and thats why I have this problem? It seems very odd.

All and any suggestions will be appreciated.
Thanks