Hi,
If you are tracking users by the session count itself, tagged users vs anonymous users shouldn't make a difference in terms of ongoing volume, as both types count towards the session count.
A few things could be going on here:
1) A natural decrease in traffic
2) If you are encountering the max number of actions configured in your tenant (https://www.dynatrace.com/support/help/platform-modules/digital-experience/web-applications/troubles...), the application may be discarding some traffic
3) Domain unification could cause this. If you have one application where users go through two domains in the same application (eg. example1domain.org and example2domain.org), this would appear as two sessions in Dynatrace despite being the same application, as first party session cookies cannot be placed across two domains. If example2domain was replaced with example1domain, all traffic would appear in one session
4) I would also validate the tag and beacons to ensure not potential issue with those
