When using parallel processing in the Groups, if Magneto II is activated in the strip,
Comb Filtering is introduced. Turn off Magneto and all is good.
This happens with the plugin interface loaded in the inserts sections as well.
Reproduce like so…
Take any audio source, audio track, vst instrument etc. (Drums are the best for this)
Route the output of the track or instrument to Group 1.
Then activate Sends 1 and 2 from the original source track and send these to Groups 2 and 3.
Now turn on Magneto on any of the 3 groups…comb filtering.
I suspect delay compensation at fault.
I found one other mention of this from 2013.
Please, if anyone can reproduce this it would be helpful.