diff --git a/tracker/tracker/src/main/app/index.ts b/tracker/tracker/src/main/app/index.ts
index 0904389f9..8b2271619 100644
--- a/tracker/tracker/src/main/app/index.ts
+++ b/tracker/tracker/src/main/app/index.ts
@@ -229,6 +229,8 @@ export default class App {
   }
 
   attachCommitCallback(cb: CommitCallback): void {
+    // TODO!: what if start callback added when activityState === Active ?
+    // For example - attachEventListener() called during dynamic <iframe> appearance
     this.commitCallbacks.push(cb)
   }
   attachStartCallback(cb: StartCallback): void {
@@ -444,13 +446,12 @@ export default class App {
         }
         this.worker.postMessage(startWorkerMsg)
 
-        this.activityState = ActivityState.Active
-
         const onStartInfo = { sessionToken: token, userUUID, sessionID }
 
         this.startCallbacks.forEach((cb) => cb(onStartInfo)) // TODO: start as early as possible (before receiving the token)
         this.observer.observe()
         this.ticker.start()
+        this.activityState = ActivityState.Active
 
         this.notify.log('OpenReplay tracking started.')
         // get rid of onStart ?
diff --git a/tracker/tracker/src/main/app/observer/top_observer.ts b/tracker/tracker/src/main/app/observer/top_observer.ts
index b3ab0e6db..47ba5fa10 100644
--- a/tracker/tracker/src/main/app/observer/top_observer.ts
+++ b/tracker/tracker/src/main/app/observer/top_observer.ts
@@ -12,7 +12,9 @@ export interface Options {
   captureIFrames: boolean
 }
 
-type ContextCallback = (context: Window & typeof globalThis) => void
+type Context = Window & typeof globalThis
+
+type ContextCallback = (context: Context) => void
 
 // Le truc - for defining an absolute offset for (nested) iframe documents. (To track mouse movments)
 type Offset = { top: number; left: number }
@@ -59,6 +61,7 @@ export default class TopObserver extends Observer {
   private readonly contextCallbacks: Array<ContextCallback> = []
 
   // Attached once per Tracker instance
+  private readonly contextsSet: Set<Context> = new Set()
   attachContextCallback(cb: ContextCallback) {
     this.contextCallbacks.push(cb)
   }
@@ -98,9 +101,15 @@ export default class TopObserver extends Observer {
           }
         }
       }
-      if (currentWin && currentWin !== win) {
-        //@ts-ignore https://github.com/microsoft/TypeScript/issues/41684
-        this.contextCallbacks.forEach((cb) => cb(currentWin))
+      if (
+        currentWin &&
+        // Sometimes currentWin.window is null (not in specification). Such window object is not functional
+        currentWin === currentWin.window &&
+        !this.contextsSet.has(currentWin.window) // for each context callbacks called once per Tracker (TopObserver) instance
+      ) {
+        this.contextsSet.add(currentWin.window)
+        //+ https://github.com/microsoft/TypeScript/issues/41684
+        this.contextCallbacks.forEach((cb) => cb(currentWin.window))
         win = currentWin
       }
     })