I use Ableton with Focusrite Scarlett 2nd gen. I'm currently using 256 buffer. I've tried using 128 but it screwed up some vocal takes I did the other day (there are 5-10 seconds of cracks in the middle of each 4 minute long complete song take). Also I froze the other tracks (eight of them, so not that many) before starting recording. No FX on master track.

Maybe I should've bought 2015 MBP then. Or maybe I should downgrade to Mojave? Or buy the Apple adapter? Or a different interface? No idea; both Focusrite and Ableton say they are compatible with Catalina.