Aqara U400 locks go offline after Nest Hub Max is powered on

I have 5 Aqara U400 locks connected to Home Assistant through Matter over Thread. All 5 locks are on the same Thread network, NEST-PAN-C21F.

My setup includes an Apple HomePod mini and a Google Nest Hub Max (Nest). My initial setup wasn't intended for the Nest to be included whatsoever. However, the goal was to have both ecosystems coexist while keeping the U400s available to both Apple Home and Home Assistant. Home Assistant’s Thread integration currently shows the HomePod as the border router for this Thread network.

To be clear, the Nest is also used every day as the primary voice assistant, so leaving it unplugged isn’t a practical solution.

Here’s the strange part: when I unplug the Nest the U400s remain online. When I plug the Nest back in, after several hours one or more random locks eventually become unavailable. Importantly, the locks do not go offline in the Aqara app or in Apple Home. They remain available there. The unavailable state appears to be specific to the Matter connection to Home Assistant.

Matter logs show subscription timeouts, failed probes, and “address is unreachable” when a lock drops.

Has anyone seen a Nest cause instability with Matter over Thread devices when an Apple HomePod is also present? Is there anything specific I should check regarding multiple Thread border routers, Thread networks, IPv6, mDNS/multicast, or VLAN configuration?

Note: I have spent days working on this with both Chat and Gemini and we still haven’t found a solution so now I'm reaching out to humans for help.

I’m attaching a screenshot of my Home Assistant Thread configuration.