Good memory indeed Rover ! The issue with my 7 is also strange, as some FSU lenses seem to have problems to screw in all the way, and some don't screw at all. Curiously, the Canons and Cosina screw perfectly, but OTH those Ruskies also screw perfectly on a 'real' Voigtlander LTM adapter.
There may be slight differences in the threads between your cameras, or maybe the threads on the lens are somewhat bent if the metal is soft, or maybe they are from the slightly different thread mount of the previous canons or maybe they were damaged at some point...
My advice, try to find a store locally with which you feel confident and tell them to lety you try to screw the lens into some ltm body if they have or into a Leica/Voigtlander/Generic LTM/M adapter otherwise and see if it presents some resistance.
If it screws perfectly in the adapter, well, then it's time to get a Leica M2 for it 😉
PS: It's always a good idea to look through the open shutter when screwing a suspicious lens. As for my own problems with the 7, I seriously think the threads on it are a bit damaged and that's the source of the problem.