Child speakers occasionally drop out in multi-room setup, when Line In input?

[walkerb]

Hey folks --

I've got 3x WiiM pros in 3 rooms, each with wired connections to a speaker setup in each rorom. It's common for me to group them together to play the same music across all 3 rooms at once.

When I'm streaming from some Bluetooth/Airplay device, everything sounds great and all the audio aligns, I'm very happy with it. (There's ~500ms latency, presumably a side effect of aligning-the-audio-between-rooms, but that's acceptable.)

I've got a record player attached to one WiiM Pro (labelled "Dining Room") via Line In. If I group my other devices to Dining Room, and play a record (I have "Auto-sensing of Line In" enabled on the Dining Room WiiM pro)...

• The Dining Room speakers, where I can follow a trail of physical wires from speakers to record player, work great 100% of the time
• the 2 other rooms' speakers work great 95% of the time, but drop out 5% of the time -- just completely go silent for a few seconds. Then ~50% of the time they'll come back fine, and ~50% of the time they'll come back slightly out-of-sync, playing a couple 100s of ms in front of / behind the Dining Room speakers. If they're out of out of sync, they get "in sync" after a couple seconds of playing out of sync.

Man, this puts a huge damper on playing records across all 3 rooms! Is there any setting I can adjust that would reduce drop-out on child devices when playing Line-In multi-room?