diff --git a/plugin-server/src/main/ingestion-queues/session-recording/utils.ts b/plugin-server/src/main/ingestion-queues/session-recording/utils.ts
index 94b930625b41d..470905f58ac2d 100644
--- a/plugin-server/src/main/ingestion-queues/session-recording/utils.ts
+++ b/plugin-server/src/main/ingestion-queues/session-recording/utils.ts
@@ -324,21 +324,29 @@ export const parseKafkaBatch = async (
             continue
         }
 
-        const session_key = `${parsedMessage.team_id}:${parsedMessage.session_id}`
-        const existingMessage = parsedSessions.get(session_key)
+        const sessionKey = `${parsedMessage.team_id}:${parsedMessage.session_id}`
+        const existingMessage = parsedSessions.get(sessionKey)
+
         if (existingMessage === undefined) {
             // First message for this session key, store it and continue looping for more
-            parsedSessions.set(session_key, parsedMessage)
+            parsedSessions.set(sessionKey, parsedMessage)
             continue
         }
 
+        // Shallow clone the eventsByWindowId object to make sure we don't mutate the original
+        const newEventsByWindowId: IncomingRecordingMessage['eventsByWindowId'] = Object.entries(
+            existingMessage.eventsByWindowId
+        ).reduce((acc, [windowId, events]) => {
+            acc[windowId] = [...events]
+            return acc
+        }, {} as IncomingRecordingMessage['eventsByWindowId'])
+
         for (const [windowId, events] of Object.entries(parsedMessage.eventsByWindowId)) {
-            if (existingMessage.eventsByWindowId[windowId]) {
-                existingMessage.eventsByWindowId[windowId].push(...events)
-            } else {
-                existingMessage.eventsByWindowId[windowId] = events
-            }
+            newEventsByWindowId[windowId] = newEventsByWindowId[windowId] || []
+            newEventsByWindowId[windowId].push(...events)
         }
+
+        existingMessage.eventsByWindowId = newEventsByWindowId
         existingMessage.metadata.rawSize += parsedMessage.metadata.rawSize
 
         // Update the events ranges