There are two possibilities here. Either the AVR is not properly initializing the new digital audio stream processing or the HDMI handshake has left the processor confused as to what form of digital audio is coming in.
I recommend you try HDMI Audio LPCM instead of either Bitstream or Auto. AVRs that have problems initializing a newly started Bitstream will often not have problems when the digital audio input is LPCM.
I also recommend you try some experiments with lowering the bandwidth on the HDMI cable. This would include turning off Deep Color in the OPPO and temporarily trying a lower resolution (1080i or 720p -- don't go lower, as the high bit rate audio tracks can not be carried on HDMI when the video resolution is lower than 720p).
If the audio works without problems at 720p or 1080i, but still fails at 1080p (or 1080p plus Deep Color), than that is strong evidence of marginal cabling. Try upgrading your HDMI cables. Keep in mind that HDMI is an end to end protocol so the problem could be the HDMI cable on the OUTPUT side of the AVR. If you have any adapters, wall plates, daisy-chained cables, HDMI switches, or other gizmos in the HDMI path, they alone could be the cause of the problem. Also note that for HDMI, too *SHORT* of a cable can give just as much problem as too *LONG* of a cable. The sweet spot length for HDMI between any two devices is 6 feet (2 meters). So an 18 inch HDMI cable could very well cause problems, as non-intuitive as that must seem. This has to do with how the HDMI chips "equalize" the signal on the cable to try to make longer cables work more reliably.
Thank you (as always!) Bob. I will give this a try and report back. FWIW, my PS3 Slim has always sent Bitstream and been set to Deep Color ON (or Auto? I forget but it is definitely not OFF) and sending full 1080P to the AVR all along, so I'll cross my fingers that a swell new HDMI cable will do the trick (mine are all 6 ft). Other than that, I may also try a different input on my AVR incase the current one is "finicky"?
One more question/This comment has me confused a bit:
Keep in mind that HDMI is an end to end protocol so the problem could be the HDMI cable on the OUTPUT side of the AVR.
In my situation, the AVR is not outputting anything over HDMI as I'm only SENDING audio signal TO it; the video is Oppo direct to my TV via HDMI 1?