iPhone HomePodMini/AirPods Max/MacBook arbitration

iPhone 16 Pro running iOS 18.5. Launch Apple Music. Select the AirPlay icon and select the pair of HomePodMinis on my desk. Press Play. Music starts.

Randomly between 1 or 429 minutes...

Let's disconnect from the HomePodMinis and start playing music on the nearby AirPods Max.

Randomly again...

The AirPods Max connect to the MacBook Pro M2 running Sequoia 15.5.

Reconnect the iPhone to the HomePodMinis, which takes about a minute for it to figure out.

Return to the top and repeat this every other day.

Any ideas on how to prevent this Bluetooth/AirPlay musical chairs? It was funny the first 15 times, but when you're in the middle of a busy workday, the last you want to do is have to help these high-end products decide who they're supposed to communicating with. If I set the first time, why would it change, all things being equal?

I have a feeling, since Apple is peerless, someone here is going to have me check if my microwave oven's interference is to blame.