Its always good to re-home your build plate after a new FEP. It could be slightly thicker or thinner then the old one. Then the build plate would be too far or to close.

Also if you did somehow F* up your build plate by sanding it you could try putting on a magnetic spring steel plate. (like this one https://www.amazon.com/KOYOFEI-Platform-Building-Magnetic-Flexible/dp/B0B1D9YYZ1/ref=sr_1_1_sspa?keywords=elegoo+mars+magnetic+build+plate&qid=1688616267&sr=8-1-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&psc=1)

I put one on my mars pro2 after I got several deep scratches on the build plate and it works great.