diff --git a/tracker/tracker/package.json b/tracker/tracker/package.json
index e5fdefddf..0c5b06634 100644
--- a/tracker/tracker/package.json
+++ b/tracker/tracker/package.json
@@ -1,7 +1,7 @@
 {
   "name": "@openreplay/tracker",
   "description": "The OpenReplay tracker main package",
-  "version": "3.5.7",
+  "version": "3.5.9",
   "keywords": [
     "logging",
     "replay"
diff --git a/tracker/tracker/src/main/modules/mouse.ts b/tracker/tracker/src/main/modules/mouse.ts
index 196a89653..b72e5dbb9 100644
--- a/tracker/tracker/src/main/modules/mouse.ts
+++ b/tracker/tracker/src/main/modules/mouse.ts
@@ -83,10 +83,6 @@ function _getTarget(target: Element): Element | null {
 }
 
 export default function (app: App): void {
-  // const options: Options = Object.assign(
-  //   {},
-  //   opts,
-  // );
 
   function getTargetLabel(target: Element): string {
     const dl = getLabelAttribute(target);
diff --git a/tracker/tracker/src/webworker/BatchWriter.ts b/tracker/tracker/src/webworker/BatchWriter.ts
index de0e956ef..5f220bbec 100644
--- a/tracker/tracker/src/webworker/BatchWriter.ts
+++ b/tracker/tracker/src/webworker/BatchWriter.ts
@@ -28,9 +28,10 @@ export default class BatchWriter {
     this.beaconSizeLimit = limit
   }
 
+  // TODO: clear workflow
   writeMessage(message: Message) {
     if (message instanceof Timestamp) {
-      this.timestamp = (<any>message).timestamp;
+      this.timestamp = (<any>message).timestamp
     }
 
     if (!message.encode(this.writer)) {
@@ -58,10 +59,11 @@ export default class BatchWriter {
     this.isEmpty = false
   }
 
-  flush(): Uint8Array | null {
-    if (this.isEmpty) { return null }
+  finaliseBatch() {
+    if (this.isEmpty) { return }
+    this.onBatch(this.writer.flush())
+    this.prepareBatchMeta()
     this.isEmpty = true
-    return this.writer.flush()
   }
 
   clean() {
diff --git a/tracker/tracker/src/webworker/index.ts b/tracker/tracker/src/webworker/index.ts
index 519deeb0f..b9640e9e2 100644
--- a/tracker/tracker/src/webworker/index.ts
+++ b/tracker/tracker/src/webworker/index.ts
@@ -2,6 +2,7 @@ import Message from "../messages/message.js";
 import { 
   classes,
   SetPageVisibility,
+  MouseMove,
 } from "../messages/index.js";
 import QueueSender from "./QueueSender.js";
 import BatchWriter from "./BatchWriter.js";
@@ -15,11 +16,10 @@ let sender: QueueSender | null = null
 let writer: BatchWriter | null = null
 
 function send(): void {
-  if (!sender || !writer) {
+  if (!writer) {
     return
   }
-  const batch = writer.flush()
-  batch && sender.push(batch)
+  writer.finaliseBatch()
 }
 
 
@@ -58,6 +58,10 @@ self.onmessage = ({ data }: MessageEvent<WorkerMessageData>) => {
   }
 
   if (Array.isArray(data)) {
+    if (!writer) {
+      throw new Error("WebWorker: writer not initialised.")
+    }
+    const w = writer
     // Message[]
     data.forEach((data) => {
       const message: Message = new (<any>classes.get(data._id))();
@@ -68,8 +72,8 @@ self.onmessage = ({ data }: MessageEvent<WorkerMessageData>) => {
         } else {
           clearTimeout(restartTimeoutID)
         }
-      }
-      writer && writer.writeMessage(message)
+      }     
+      w.writeMessage(message)
     })
     return
   }
@@ -100,8 +104,14 @@ self.onmessage = ({ data }: MessageEvent<WorkerMessageData>) => {
   }
 
   if (data.type === "auth") {
-    sender && sender.authorise(data.token)
-    data.beaconSizeLimit && writer && writer.setBeaconSizeLimit(data.beaconSizeLimit)
+    if (!sender) {
+      throw new Error("WebWorker: sender not initialised. Recieved auth.")
+    }
+    if (!writer) {
+      throw new Error("WebWorker: writer not initialised. Recieved auth.")
+    }
+    sender.authorise(data.token)
+    data.beaconSizeLimit && writer.setBeaconSizeLimit(data.beaconSizeLimit)
     return
   }
 };