Hi, thanks for your reply. I was able to test the headphones with the splitter on another machine. When I ran audacity for that, I could see that the mic input was only happening for one channel on that as well, so its my guess that it is the splitter that is causing the issue. I purchased a USB audio adapter that accepted TRRS, so didnt need the splitter, and this did the job.
The plugable device will sit in the draw for another day then…