I can replicate this now here. The timing of every nth note is shifted by some samples. This only happens when routing the MIDI output of a VSTi to some other VSTi. It does NOT happen when routing the MIDI output of a VSTi to a sample in Renoise.
Unfortunately it will take a longer while to figure out what’s happening here, but I’m on it.
I also still can’t replicate the other issues mentioned here. @gentleclockdivider Did you manage to run the tests with the loopback device at the end?
Probably someone else could help testing this issue as well (MIDI input jitter).