Iphone remote app stopped controlling receiver volume

So this is something that has worked for years. I have a 4k appletv hooked up via hdmi to a Marantz sr7015 receiver.

Previously, if I opened the remote app on my iPhone, the side volume buttons on the phone would control the volume on the receiver. This worked, and then stopped working at some point last year (I believe it broke with tvos 15.4 or 15.5). It then was fixed in tvos 15.6 and all was great until the apple tv updated to 16.0. It is now broken again.

The version numbers could be a coincidence and not actually related, but the timing of this function working and not lines up.

Also, this was working a few days ago from both my iphone 13pro and my iPhone 14 pro, both running ios 16.0.1. Yesterday is when my apple tv updated and when the volume control stopped.

Volume control via the silver apple tv remote still works (and it's not occurring via IR -- I've tested it from another room behind closed doors while completely covering the remote).

Volume control from my iPad running 15.7 also does not work.

I'm pretty sure this isn't a setting issue, but I have toggled the various hdmi control options off and on again just to cover my bases.

Has anyone else seen this? It doesn't seem like something that would be specific to my receiver, but i suppose you never know.