When I have the BBD effect and enable CLK sync to an external midi clock, it sounds like the TIME parameter is constantly modified, giving the BBD the traditional pitch swirl. I thought I had an LFO modulating the FX Time, but no.
Several components involved, so it is hard to nail it down. This is my setup:
Windows 10
Ableton Live
Focusrite Scarlett 18i20 (v3)
DIN MIDI -> Take 5
When I select the Global Clock mode = Out, it is stable, but when I select In to sync to Ableton, the pitch of the BBD echo starts modulating.