I've run into an issue with my bdp-83 as well. This may or may not be related to your problem but it may help. Mine is having a problem loading the top menu on discs primarily from Universal Studios, Killer Elite and Change Up. It would download trailers from the internet and play trailers directly from the disc but not load the menu. I checked and it had the latest update available.
I e-mailed oppo's customer support about the problem early on superbowl Sunday. The response was time stamped during the superbowl. Now that's dedicated customer service. They have an update that they are beta testing that should resolve the issue. Sorry I don't have the link available to post at present, at work. I'm sure if you contact oppo's customer support they will give it to you.
Hope this helps.
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Marantz AV7702 mkII
Outlaw Model 7125, Outlaw Model 2200 (3)
LG OLED C8
Oppo BDP-83, LG UBK90 4k
Directv, Sony PS4 Pro/PS3
Polk Audio RT800, CS400, FX500
SVS Elevation (4)
Sunfire True Subwoofer, Epik Empire
APC H15
Harmony Elite remote
Blue Jeans and Monoprice interconnects