Harmony remote - changing volume stops casting (chromecast ultra)

Interesting issue. I have a Harmony Companion remote and the app on my phone. Whenever I use either the app or the remote to change the volume on my receiver, whatever is being cast stops. I've tried both Plex and Netflix from both my desktop PC and my phone.

Anyone have this issue before?

Items being used:

Harmony companion and app

Chromecast Ultra plugged into receiver

Sony STR-DN840 receiver

edit: ended up having nothing to do w/ Harmony, same issue with main remote. Thanks u/theychx, turning off 'pass through for HDMI' in the receiver's settings solved the issue.