QM8K 98 not consistently passing through audio

Set up is a 98" QM8k. Most recent Apple TV. Sonos Arc Ultra. Most recent firmware on everything. When using the Apple TV, Netflix and Apple TV+ outputs Dolby atmos, but the other apps output stereo. However, if I change the audio output to passthrough, instead of auto, then I get multi channel 5.1 in all apps. But this doesn't solve my problem because when I watch ATSC 3.0 antenna content on passthrough, I get stereo audio, but when I switch audio output back to "auto" I get full surround output. Has anyone else encountered this? I feel like I'm going insane.