I have had problems with that 10th frame too.
Usually it goes like this: I glance at the sheet and notice that I'm doing great/lousy, whichever it is at the time, at just that moment I totally lose my concentration thinking the game is already over, let go a big whew, and then I go ahead and make a miserable shot.
It has a lot to do with self-confidence, at least in my case, one is afraid both to do too well, or too bad, and once you're doubtful the frame is practically lost.
It might help you, as it did help me, to ignore the scoresheet and just bowl practicelike until somebody stops you

Tiller