question for Tap Pap users

Hi all, I have been using Tap Pap for about 10 months with no big problems. I have two of the new model mouthpieces, one set tighter on my teeth than the other, and switch them out every other night.
The last couple of weeks, both lips have had a weird feeling, a bit like after you have had a novocain injection and it has almost worn off. Not really painful, sort of a mild combo of sunburn and numbness, if that makes any sense. When I drink something fizzy or acidic, like seltzer or wine, my lips sting a bit.
Have any of you Tap Pap users every experienced this?
It might have nothing to do with the Tap Pap, but I should rule it out first, as that seems the most likely source. I don't see anything red or irritated-looking when I look inside my lips.
Thanks.

Have you changed the washing...different cleanser for the mask? Have you eaten something that would affect your lips?

You may be allergic to the material of the device and need to consider other types that would at least allow you to also wear Pad-a-Cheek liners underneath to keep them from touching your skin.

Thanks for replies so far. I am testing a few things and will report back.