diff --git a/android/app/src/main/java/com/fabledsword/minstrel/player/output/OutputPickerController.kt b/android/app/src/main/java/com/fabledsword/minstrel/player/output/OutputPickerController.kt
index 130b0bbf..1160653f 100644
--- a/android/app/src/main/java/com/fabledsword/minstrel/player/output/OutputPickerController.kt
+++ b/android/app/src/main/java/com/fabledsword/minstrel/player/output/OutputPickerController.kt
@@ -1,3 +1,4 @@
+@file:Suppress("TooManyFunctions") // 5 MediaRouter.Callback overrides inflate the count
 package com.fabledsword.minstrel.player.output
 
 import android.content.Context
@@ -11,7 +12,6 @@ import com.fabledsword.minstrel.player.StreamTokenProvider
 import com.fabledsword.minstrel.player.output.upnp.RenderingControlClient
 import com.fabledsword.minstrel.player.output.upnp.SoapClient
 import com.fabledsword.minstrel.player.output.upnp.UpnpDiscoveryController
-import com.fabledsword.minstrel.player.output.upnp.sonos.SonosZoneGroup
 import dagger.hilt.android.qualifiers.ApplicationContext
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.flow.MutableStateFlow
@@ -20,6 +20,8 @@ import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.combine
 import kotlinx.coroutines.flow.stateIn
 import kotlinx.coroutines.launch
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
 import okhttp3.OkHttpClient
 import timber.log.Timber
 import javax.inject.Inject
@@ -86,17 +88,17 @@ class OutputPickerController @Inject constructor(
     private val systemRoutesInternal = MutableStateFlow(snapshotFromRouter())
 
     private val selectedUpnpRouteIdInternal = MutableStateFlow<String?>(null)
-    private var lastKnownRemotePositionMs: Long = 0L
+    private val selectUpnpMutex = Mutex()
 
     val routesState: StateFlow<RouteSnapshot> = combine(
         systemRoutesInternal,
         upnpDiscovery.routes,
         upnpDiscovery.sonosTopology,
         selectedUpnpRouteIdInternal,
-    ) { sys, upnp, topology, upnpSelected ->
-        val suppressed = nonCoordinatorMemberUdns(topology)
+    ) { sys, upnp, _, upnpSelected ->
+        val suppressed = upnpDiscovery.nonCoordinatorMemberUdns()
         val visibleUpnp = upnp
-            .filter { it.id.removePrefix("uuid:") !in suppressed }
+            .filter { it.id.removePrefix("uuid:") !in suppressed } // suppressed set is bare UDNs
             .map { OutputRoute.fromUpnpRoute(it) }
         val merged = sys.available + visibleUpnp
         val current = if (upnpSelected != null) {
@@ -107,12 +109,6 @@ class OutputPickerController @Inject constructor(
         RouteSnapshot(current = current, available = sortRoutes(merged))
     }.stateIn(scope, SharingStarted.Eagerly, systemRoutesInternal.value)
 
-    private fun nonCoordinatorMemberUdns(topology: List<SonosZoneGroup>): Set<String> =
-        topology.flatMap { g ->
-            g.members.map { it.udn.removePrefix("uuid:") }
-                .filter { it != g.coordinatorUdn.removePrefix("uuid:") }
-        }.toSet()
-
     private val callback = object : MediaRouter.Callback() {
         override fun onRouteAdded(router: MediaRouter, route: MediaRouter.RouteInfo) =
             refresh()
@@ -189,14 +185,14 @@ class OutputPickerController @Inject constructor(
         val wasUpnp = selectedUpnpRouteIdInternal.value
         if (wasUpnp != null) {
             val active = activeUpnpHolder.active.value
-            lastKnownRemotePositionMs = remoteState.positionMs
+            val capturedPositionMs = remoteState.positionMs
             val wasPlayingRemote = remoteState.isPlaying
             scope.launch {
                 runCatching { active?.avTransport?.stop() }
                     .onFailure { Timber.w(it, "UPnP Stop failed during disconnect") }
                 activeUpnpHolder.set(null)
                 selectedUpnpRouteIdInternal.value = null
-                playerController.seekTo(lastKnownRemotePositionMs)
+                playerController.seekTo(capturedPositionMs)
                 if (wasPlayingRemote) playerController.play()
             }
         }
@@ -214,11 +210,11 @@ class OutputPickerController @Inject constructor(
      * the cause in logcat (OkHttp's logger doesn't cover our own
      * deserialize / SOAP-parse code paths).
      */
-    private suspend fun selectUpnp(route: OutputRoute) {
+    private suspend fun selectUpnp(route: OutputRoute) = selectUpnpMutex.withLock {
         val trackId = playerController.uiState.value.currentTrack?.id
         if (trackId == null) {
             Timber.w("UPnP select skipped: no currentTrack (start playback first)")
-            return
+            return@withLock
         }
         // Honor Sonos topology: pick the coordinator's route when the user
         // tapped a group row. Suppression in routesState already keeps the
@@ -232,7 +228,7 @@ class OutputPickerController @Inject constructor(
                 "UPnP select skipped: no transport for route id=${effectiveRoute.id} " +
                     "(route disappeared or id mismatch with discovery list)",
             )
-            return
+            return@withLock
         }
         val rendering = renderingClientFor(effectiveRoute.id)
         selectedUpnpRouteIdInternal.value = effectiveRoute.id