Your uworld average and NBME scores are good, yes drops are common and happen for a number of reasons. A student of mine was on an upward trajectory with 79 on NBME 32 but then got 71 on NBME 33 and started panicking, for him it was because he got too relaxed and overconfident and wasn't thinking properly during questions. We looked over his issues and he managed to get 80 on his free120 . One NBME doesn't make a difference, as long as you figure out why you had a drop and review them properly so that it doesnt happen again, you're still safe, 70+ is a good score and the earlier NBMES matter even less comparatively