Your software
My Mautic version is: v2.15.3
My PHP version is: 7.2.34
Your problem
My problem is: If I go to “contact segments” I have 8894 contact in a “newsletter” segment. When I want to send an email to this segment it will only use 7159 contacts.
You can do it through reports. You would create a new report with Data Source “Email Sends” and then add in your segment and bounce+unsubs in the filter field.