diff --git a/server/routes/webhook.js b/server/routes/webhook.js
index 483c27c..0dce65f 100644
--- a/server/routes/webhook.js
+++ b/server/routes/webhook.js
@@ -43,9 +43,11 @@ function pruneReplayCache() {
   }
 }
 
+// Prune the replay cache once per minute
+setInterval(pruneReplayCache, 60 * 1000).unref();
+
 function isReplay(eventType, instanceName, eventDate) {
   if (!eventDate) return false;
-  pruneReplayCache();
   const key = `${eventType}:${instanceName || ''}:${eventDate}`;
   if (recentEvents.has(key)) return true;
   recentEvents.set(key, Date.now());
@@ -237,24 +239,23 @@ router.post('/sonarr', webhookLimiter, (req, res) => {
 
   const { eventType, instanceName, eventDate } = validation;
 
-  if (isReplay(eventType, instanceName, eventDate)) {
+  const sonarrInstances = getSonarrInstances();
+  const inst = sonarrInstances.find(i => i.name === instanceName || i.id === instanceName) || sonarrInstances[0];
+  const resolvedInstanceName = inst ? inst.name : instanceName;
+
+  if (isReplay(eventType, resolvedInstanceName, eventDate)) {
     logToFile(`[Webhook] Sonarr duplicate event ignored: ${eventType} @ ${eventDate}`);
     return res.status(200).json({ received: true, duplicate: true });
   }
 
   try {
-    logToFile(`[Webhook] Sonarr event received - Type: ${eventType}, Instance: ${instanceName || 'unknown'}`);
+    logToFile(`[Webhook] Sonarr event received - Type: ${eventType}, Instance: ${resolvedInstanceName || 'unknown'}`);
     logToFile(`[Webhook] Sonarr payload: ${JSON.stringify(req.body)}`);
 
     // Phase 5.1: update webhook metrics for polling optimization
-    // Note: instanceName from webhook is often generic (e.g., "Sonarr"), not the configured name
-    // Update metrics for all Sonarr instances since we can't reliably match
-    const sonarrInstances = getSonarrInstances();
-    if (sonarrInstances.length > 0) {
-      for (const inst of sonarrInstances) {
-        cache.updateWebhookMetrics(inst.url);
-      }
-      logToFile(`[Webhook] Updated metrics for ${sonarrInstances.length} Sonarr instance(s)`);
+    if (inst) {
+      cache.updateWebhookMetrics(inst.url);
+      logToFile(`[Webhook] Updated metrics for Sonarr instance: ${inst.name} (${inst.url})`);
     }
 
     // Phase 2: background cache refresh + SSE broadcast (fire-and-forget)
@@ -290,24 +291,23 @@ router.post('/radarr', webhookLimiter, (req, res) => {
 
   const { eventType, instanceName, eventDate } = validation;
 
-  if (isReplay(eventType, instanceName, eventDate)) {
+  const radarrInstances = getRadarrInstances();
+  const inst = radarrInstances.find(i => i.name === instanceName || i.id === instanceName) || radarrInstances[0];
+  const resolvedInstanceName = inst ? inst.name : instanceName;
+
+  if (isReplay(eventType, resolvedInstanceName, eventDate)) {
     logToFile(`[Webhook] Radarr duplicate event ignored: ${eventType} @ ${eventDate}`);
     return res.status(200).json({ received: true, duplicate: true });
   }
 
   try {
-    logToFile(`[Webhook] Radarr event received - Type: ${eventType}, Instance: ${instanceName || 'unknown'}`);
+    logToFile(`[Webhook] Radarr event received - Type: ${eventType}, Instance: ${resolvedInstanceName || 'unknown'}`);
     logToFile(`[Webhook] Radarr payload: ${JSON.stringify(req.body)}`);
 
     // Phase 5.1: update webhook metrics for polling optimization
-    // Note: instanceName from webhook is often generic (e.g., "Radarr"), not the configured name
-    // Update metrics for all Radarr instances since we can't reliably match
-    const radarrInstances = getRadarrInstances();
-    if (radarrInstances.length > 0) {
-      for (const inst of radarrInstances) {
-        cache.updateWebhookMetrics(inst.url);
-      }
-      logToFile(`[Webhook] Updated metrics for ${radarrInstances.length} Radarr instance(s)`);
+    if (inst) {
+      cache.updateWebhookMetrics(inst.url);
+      logToFile(`[Webhook] Updated metrics for Radarr instance: ${inst.name} (${inst.url})`);
     }
 
     // Phase 2: background cache refresh + SSE broadcast (fire-and-forget)