After installing fresh firmware, one should always do a factory reset.
If it is ONLY newer discs, then I'd say it is a firmware issue. Are all of the discs that won't play from the same company? (FOX?) In talking with Oppo, they said Fox is notorious for changing their decoding codec frequently and that required small tweaks to get some discs to work correctly. I am sure Fox isn't the only one, but that's a possibility. I've not had a disc that my BDP79 wouldn't play so far, but it is also a newer player. I bought my parents the 220 last year and they haven't reported any issues yet.