Those are a lot of fun to play with! Glad you got it working! Textured PEI sheets are great for PLA in general. Usually a good wipe with isopropyl alcohol before a print works to keep the adhesion strong. I find every once in a while actually washing and scrubbing it with dish soap and hot water is needed to refresh the PEI surface.
Probably have to scrape it off with a razor blade. You might try acetone as a last ditch solvent method, but that’s it’s own bag of worms.