I often get weird issues using the ARC, and have never tracked it down. I don't know if it is the audio device of the TV. Randomly, the audio will get all distorted for a random amount of time, and then suddenly it snaps back to normal. I never looked into the format to see if there's some sort of re-sync signal sent periodically that is part of ARC, but that would make sense to me based on observed behavior. When the audio gets weird, it's sounds like some sort of sample rate issue as the sound changes pitch, plays distorted, and goes out of sync with the video.
My TV and audio equipment happen to have an optical connection and after switching to that away from ARC, the issue has gone away.
I had perfectly working eARC for over a year until I started getting random audio dropouts. After months, I figured out they were due to my Wii U coming out of standby and checking for updates on a different HDMI port. I think it worked fine before a firmware update to either my TV or my soundbar. Works fine again after disabling the Wii U's background updates.
My TV and audio equipment happen to have an optical connection and after switching to that away from ARC, the issue has gone away.