I just had this happen last week.
I let the reels air dry, and 24 hours is not enough. They need 48. Of the two i used previously, there was some water, as in a few drops, still in the other reel i did not use this time, so that is how i know they were still "wet". Was water the problem.? I do not know. I did not run dead film through the reel first, like i normally each time do before i load "real" film.
I tried tapping, banging the reels, but that did not work...tried pulling apart just a bit and that did nothing to help...i twisted them in two and reloaded the film, and it did it again at about the 70% mark.
What i did, for the first time, was to "short stroke" the reels. I only gave them a twist that was about 10-20% of their normal travel. Doing this, i was able to load the film all the way, and get those last 3-5 frames.
Who knows.......