multiroom-server fails to start on Pi 3 — port conflict with multiroom-client on fresh install

I’m running balenaSound 3.11.0 on a fleet of Raspberry Pi units. Two of them (living room server and kitchen) work correctly. The third unit (bathroom, Pi 3B) consistently fails to start multiroom-server due to a port conflict with multiroom-client.

The problem

On every boot, multiroom-client starts before multiroom-server and claims ports 1704, 1705, and 1780. When multiroom-server then tries to start, it fails with:

driver failed programming external connectivity on endpoint multiroom-server: 
Error starting userland proxy: bind 0.0.0.0:1705: address already in use

This makes the supervisor enter a locked state, making remote reboots impossible. The only workaround is manually stopping multiroom-client via terminal, starting multiroom-server, then restarting multiroom-client — every single boot.

Setup

  • Hardware: Raspberry Pi 3B

  • balenaSound: 3.11.0+rev1

  • SOUND_MODE: MULTI_ROOM

  • SOUND_DISABLE_BLUETOOTH: 1

  • AUDIO_OUTPUT: alsa_output.platform-3f00b840.mailbox.stereo-fallback

  • BALENA_HOST_CONFIG_dtoverlay: vc4-fkms-v3d,cma-320

  • SNAPCAST_SERVER: 192.168.129.10 (fixed IP of server unit)

What I’ve tried

  • Fresh reflash of SD card — problem persists

  • Manually stopping multiroom-client before starting multiroom-server — works but not persistent

  • Restarting balena_supervisor — sometimes helps temporarily

Question

Is there a way to enforce startup order so multiroom-server always starts before multiroom-client? Or is there a configuration to prevent multiroom-client from exposing ports 1704/1705/1780 on client-only units?