Oppo 103D streaming issues

Did you try re-booting the unit, un plug the Oppo and press each button on the front panel to drain any stored capacitance. The see if it works better, sometimes all components with micro processing will need a full capacitance re-boot, or at least in my experience.
Also even if your TV works fine, I would unplug the modem and router and see if that makes a difference. Finally, if you have a spare Ethernet cable try it, it may be the culprit. But unless the cable gets moved in cleaning etc, I doubt it just failed and the fact that it makes a connection then doesn’t seems to be very low chance, in my opinion. Good luck, and if you have to send it to Oppo, please share that experience with us, now that they are out of the DVD player biz.

Just wanted to offer a quick update here. I believe I have found the resolution. I read on another forum that it is necessary to return to the factory default settings following a software update. I did that and now it seems to be working fine again. The unit will retain your internet connection settings when this is performed.

I’m curious.  Given the low resolution of You Tube sound, does it actually sound better coming through the 105 compared to the TV as a source?  Is your TV hooked up to your pre amp or are you using the TV speakers?

It's actually a 103D. I run the coax out to my DAC which feeds my pre-amp so I run it through my main system. The audio quality varies on Youtube. I was listening to an "audiophile" recording of music last night and it was actually pretty decent. Most of the audio is so-so however. My Oppo is only used for DVD video/audio. I use a separate CD transport for serious listening.

Make sure your Oppo is well ventilated, and that it isn't sitting right on top of a heat generating device! :)