What was the software you used to play the Blu-Rays prior to this?
As it sounds like potentially a certificate revocation list was hard written to the drive’s internal memory either by a new(er) disc you inserted or perhaps even the firmware update itself which is causing the playback software you once used (for example, PowerDVD, which requires its own decryption certificate) to fail to work, since the drive with its newly updated certificate revocation blacklist is telling it to ignore such old certs. These certs are periodically ‘retired’ by design in an attempt to curb ripping from what I gather.
Someone more knowledgeable can clarify if I’m getting any details incorrect here or if there’s another potential reason. That’s just my hunch.
If this is indeed the reason the practical solution would be to either update the playback software so it can obtain a newer AACS certificate or use one of the standalone decryption programs to decrypt the discs for playback.