If it’s only happening in reaper after testing with ableton I would probably focus my efforts there but I can’t imagine what it is other than incompatibility with the plugin itself. I mean there could definitely be some settings in there that I’m not aware of because I don’t have any experience with reaper, but maybe some of the same issues others faced with different elektron gear will be relevant.
This person notes that sync is an issue, and they made some seemingly useful observations.
it also looks like they made a video that explores their method of multi-channel recording.
I would at least scan those for a source of potential conflicts which may ultimately be relevant to the AH as well.