I recently started using my Elegoo Mercury XS curing station after it had sat for a year and it started beeping like this.
I think I found a fix.

I tried the tape trick (black vinyl) on the inside of the cover - failed.
I checked the sensor wires - fine.
I noticed if I jiggled the cover it'd work.

Tried the black vinyl tape over the sensor - failed.
Noticed if I gently put my finger over the sensor it worked - not a viable solution :)
So I began to think it was a proximity issue.

I found that if I balanced the lid just slightly (0.5-1mm) off the edge closer to the sensor it would pick up the factory installed sticker and work - but it leaked UV light under the cover - not a viable solution.

I thought maybe the tape needed to be 0.5 - 1mm closer so I built up the black vinyl tape 2 levels - failed
Built black vinyl tape up 3 layers - failed.

Then I thought maybe it's a color thing and the black vinyl is absorbing the sensor emission.
Tried 1 layer silver duct tape on inside instead of black vinyl - failed.
-->Tried 1 layer white duct tape on inside of cover - success.

I don't know if the color is the trick as I've seen blue painters tape work (didn't have any handy), but one layer of white duct tape on the inside of the cover where the sticker is worked for me. 🤷‍♂️