Hi @wenjuan_xie
Most of the time, a single visit ID and also a single visitor ID should respond to a unique user. But this can be wrong in some misconfiguration of Matomo.
Same browser configuration + IP (eg. users belonging to the same company, who have same computer types and use the same outgoing IP of with a proxy misconfiguration on your side) with no cookie tracking could be interpreted by Matomo as the same user…
@scamp, can you compare the rows displayed in your first post with the raw data Matomo used to track? (either server log or Matomo verbose log)
We have the same issue and are investigating this with Matomo support.
A not logged-in user has a visit, then he logs in and gets a new visit. And when he logs out he returns to the first visit. So it seems like there is something going wrong with merging the before and after visits to one visit.
(We already fixed the after logout by getting the userid differently, but that’s only a work around and not a good fix).