I had the same exact problem with a clutch last year and finally found the reason to be the fork pivot was cracked and moving. Car would start getting very difficult to get in gear and after pulling trans one PP finger would be sitting about .250 lower than the other two.

Bought a heavy duty one from Wayne Brewer and haven't had the issue again. I had sent the PP back three times before figuring out what it was. Always one finger lower than the others.