Parking sensor false positives, possible surface damage?

I'm having issues with the rear left parking sensor, whenever i'm in reverse it gives a false positive that something is close, which gives a red display and lots of noise. I had a look at it and it looks like a fleck of the cover has come off, and you can see a small white patch. Could that cause this, and is it possible to fix with paint or anything like that?

I saw a similar thread about parking sensor problems here: https://www.briskoda.net/forums/topic/531406-parking-sensor-problems-2019-octavia/ , which sounds like a similar issue. The suggestions there were about possible battery issues and to run a CCA test.

Could fixing the cover damage help, and how? And otherwise how easy is it to do a CCA test, or any other suggestions?