Joel, thanks for this post; a friend referred me to it. Yes, I HAVE seen this. When I started using the 20th Century reel, it worked well. But in the time since, I've also been seeing air bells on some negatives (generally 120 film), and worked to make my inversions less aggressive — more like orbital motions than a true full inversion. Apparently, at least for these 20th Century reels, a big mistake, as I began to see precisely what you described and showed, much to my dismay. I simply didn't make the connection.
But as I kept seeing this, I had to get to the bottom of it, and it indeed does seem that these reels require full-on, complete inversions, and I guess if I'm worried about bubbles forming in the solution, I'll use more solution...
Good to see I'm not alone in this, although it does make me want to try a Stearman, MOD54, or something else at this point.