Problem with firebase analytics - fine in debug but no traffic when on preview/live

I’ve set up Firebase config and debug is working brilliantly at tracking events being fired in to analytics.

When playing the game live, on either the preview or live link, I am not getting any traffic/events being recorded.

I am seeing a network warning in console for:
Unable to update session cookie
Unable to set cookie

I have the Splash enabling analytics then Trigger event such as:
Trigger Event “My event” with argument “”

Which works perfectly in preview with debug (sending events etc into the Firebase and GA4 debugview).

But then no traffic in realtime when live?