DVD player will not play certain discs

I am running 10.14.6 on a macbook pro. I think disc player is 6.0. I have the complete set of Star Trek Deep Space Nine episodes which work fine until I get to seasons 6 and 7. At this point I insert any disc which opens to solid black and the controls. Neither the controls nor the top menu do anything except give me a 'not permitted' message. Eventually the disc stops spinning but I can eject it with no problem. I had problems with these same discs before (these are professional discs) but fiddled with the top menu until they started working. Now I have a new OS and I have not played them for a while. Disc utility labels the disc as unknown/universal disc format. They worked before.

Any help would be appreciated.