I had a Yamaha receiver and a Phillips sound bar, then an lg tv and TCL android tv. No combination of amp and soundbar has worked well using arc, every one has some form of issue.
The Yamaha receiver hates DD+ codecs and refuses to play them 95% of the time.
The Phillips soundbar doesn't power on and off properly using arc and is unreliable finding its source.
I ended up using optical on them both. The best combination was lg tv to the Yamaha where k managed to fudge it and it got confused so controlled like arc but transmitted over optical.
I've just got a JBL 1000 waiting to be opened today so let's see if eARC performs any better for me.
Can I ask what model AVR you have? That must be a VERY old Yamaha AVR if it doesn't handle Dolby Digital Plus...
Did you update the firmware?