I had problems with some symptoms sometime 2nd week of September and was somehow given a solution and my Traktor Pro 3 and S4 Mk3 ran reliably for a month plus until last night it just crashed. Disappeared on a hot set (of course the music was gone) there was no crash or incident dialogue that came up. I re-booted and everything was fine. Mysterious.
I'm using a Late - 2013 Macbook Pro Retina running on Catalina and Traktor S4 Mk3. I use an external drive for extra library (Laptop can only go 250 Gb)