GDPR mandates that all personal data regarding the data subject should be erased once the purpose for processing is completed. One of the few exceptions being legal purposes.
The same principle is followed in Browser Security Plus as well. Upon deletion of technicians, Browser Security Plus will not retain any personal data except for the user name of technicians. Since a technician would have carried out certain tasks using the Browser Security Plus server (eg. deploying browser settings to a computer), it is essential for audit and legal purposes to maintain a log of the tasks carried out by that particular technician.