Loose clear retainer on one side. more details...?!

I've had my braces off for at least 3 years now. I've had the same top ones since then. I got my wisdom teeth out mid August so I don't have those to shift anything now and for the past several months I've been told that I can wear them just one night a week now. Last week (give or take a couple days) they felt fine, but tonight I put them in and the top ones are kinda loose on the left like they hang down a little and I can push them up. The retainer doesn't seem to be warped, but idk how it could be this different this quickly.
I admit a while back I had to replace my bottom retainer after getting lazy when wearing them, but my top ones seemed fine not too long ago. I'm partially wondering if it's because they're so old or something or what the problem could be.