I have s12's with a 2 pin utws5. They can't rest on my ear without pulling the earbuds just barely enough out of my ear to break the seal. I would recommend the mmcx utws5's with a mmcx to 2 pin adapter. This will allow the earbuds to pivot so you can rest the utws5 on your ears like they're designed for.

I have other 2 pin iems that work fine with the 2 pin utws5. Just the s12's give me this issue.