There has been a long running edge-case in our analytics browser SDK where user data is erroneously being written to one cookie and read from another (e.g.: being written to example.com and then being read from .example.com).

This causes user profile data to constantly be reset, resulting in issues such as session_end events being sent on every page view (causing sessions to start and end on every page visit) and Event ID being reset back to an old value on every page view, resulting in the same IDs being recycled repeatedly. The bug causing this has now been fixed in the latest version of the SDK, with additional safeguards to ensure the SDK won't read from and write to multiple different cookies.

The fix is released in version 2.33.4 of analytics-browser and is also available in the latest Google Tag Manager template (requires an upgrade via Google template gallery).