Apparently, this goes back to well before I started playing in early 2016, but I finally had to report this. I looked around, and there were discussions in the general forums that go back to 2015. Daggerfall Banker sometimes fails to appear in the bank. If I see her name hotspot, I know she'll eventually appear, but if there's no hotspot, she won't ever appear. I see other PC's all around the spot that she's not appearing at, apparently interacting with her. I have tried exiting/reentering the bank, and also tried /RELOADUI, neither of which force her to appear. When she's missing, the only thing I can do is to log out/in, and she comes back. This doesn't happen every time I access the bank, and maybe not even daily, but I'd say that it does happen several times each week, so that's pretty frequent/consistent.
I may have seen this on other NCP's but nobody with the regularity of the Daggerfall Banker. I also can't state for sure, but it does seem to happen more often when I log in to a character that's already in the bank, rather than a character that's entering the bank and didn't just log in, but it does happen both ways.