Recently I've been having the following problem shown below where I print a number of parts successfully - and they turn out great, but there is a thin layer of partially cured resin on the FEP of my Vat. I have an Anycubic Photon Mono X. When I first started using the printer about 3 months ago I had the problem but it seems to go away after a while, and I could run successive print jobs without cleaning the vat. Now the problem is back. I've read about others having this issue and have check a number of things. First, I did a calibration test to see the condition of my LCD. It seems fine and don't see any burn-out or irregularities. Next, I check my build plate home/zero position - and re-ran a job, but that didn't help.
I suspect and fear that the problem could be due to the fact that I recently had to replaced the polarizing filter on my LCD. I did adjust/install it correctly by angling it properly to block the most amount of UV light and observing that before I cut it and mounted it. It doesn't have adhesive but is mounted with the surround electrical tape. I think the problem might be that the filter I purchase is not as effective at blocking light as the factory-installed filter that comes with the 4K LCD panel from Chitubox?