Varying visits in same past month

Support & Bugs
1

We are using the selfhosted version of Matomo and are facing following issue:

  • We checked on the 11th of July with the standard All data segment the visits for June: 584 visits
  • We checked again on the 26th of July with the standard All data segment the visits for June: 601 visits

Is known if and why visits from already past month can vary?

Thanks a lot in advance!
Moritz