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I have a WH16NS40 drive that I flashed over a year ago and now all of a sudden it can't read blu rays or 4K discs but can read DVDs and blank bd-rs (even bd-r dl). Any idea what the issue is or how to fix this?

How exactly does the issue manifest though? Do you see the BD / UHD BD being recognized in the OS?

I wonder if the fact that it can recognize a blank disc really rules out that the blue laser is somewhat dead. Do you have any burned disc that you can test? Or can you afford to burn a disc and read back for testing?

Power off the drive for 5 mins
If that don't work clean the lasers
After that you are probably out of luck it would need some sort of repair probably