I see. It's the black thingy behind the clip that is causing problems.

The original straps do not have such a thing. The clip sits very securely over the lug, without any fear that it might accidentially come off. The spring plate, fitting behind the lug, does not need an additional locking device to keep it in place.
I don't really understand why the Op/Tech clips would need a locking thing. Perhaps it would be best to find an old Hasselblad strap, snip off the clips, and fit those on an Op/Tech strap?