^ I think you'll have to go to OPPO Tech Support with this one. You aren't doing anything unusual, so this shouldn't be happening. Tech Support typically monitors their email even when the office is closed on weekends and holidays.
While you are waiting, the only thing I can suggest is the general nostrum for whenever the player starts doing something funky: Do a complete Reset. Like this:
1) Remove any disc from the tray.
2) Save your Settings to a USB stick: Setup > Device Setup > Configuration Management
3) Erase Persistent Storage. Then Reset Factory Defaults. It's OK to do the Reset version which preserves account credentials, so you won't have to re-enter those afterwards.
4) Power off the player -- as always, do a normal power off. I.e., don't just cut off wall power suddenly via some sort of external, power management device.
5) Unplug the player from wall power. While still unplugged, press and hold the power button for a few seconds. This is to discharge any residual power and make sure even the lowest level of the player hardware has to reboot afresh.
6) Plug in, power up, and reload your Saved Settings from the USB stick.
7) Power down once more. Settings are saved during the power down cycle.
The only other thing you might want to try is to re-install the current firmware. You can do that by downloading a fresh copy of the version for install from a USB stick. When you power up, if not offered the choice automatically to re-install, you can initiate it from Setup > Device Setup > Upgrade
One other thing that occurs to me, if your OPPO has a "Region Free" hardware modification, consider disconnecting that to see if it is the culprit. You may have to re-install the firmware after disconnecting the 3rd party hardware mod.