Been working in El Capitan since Thursday. I can confirm the troubles with the kerning window. Otherwise, the only problem I run into is the occasional small UI glitch because of the new font. E.g., the style linking check marks in the Font Info look a bit off, but still work.
My Glyphs 2.2b (814) keeps quitting suddenly, while I’m just drawing paths. I’m running on El Capitán. Are you aware @GeorgSeifert? or is just happening with me?