Been trying to get back into Renoise a bit after ages, experimenting around, i found some issues and solutions that might help others having similar problems.
First of all are “audio enhancements / signal enhancements” on soundcards, while some games require it (like forza horizon 4), it messes up the stereo signal in Renoise completely, so always check this first and turn it off.
I had some issues with some severe laggy VST’s, turned out that fancy “game mode” in windows 10 was the cause, so also turn it off
A strange problem, some VST’s require activation or registration by drag&dropping license files in them. i can’t get this to work in Renoise 64bit version, however it works fine in Renoise 32bit version. I don’t know the cause, but this is a workaround, drag&drop vst works in renoise 32bit.
(EDIT : Small update on this one, disabling Administrator mode when starting Renoise also helps sometimes)