The log files for version 3.x are under %LocalAppData%\SafeExamBrowser\Logs. In the client logfile for that session, you should find the reason why the lock screen was activated (probably an attempt to switch the active Windows user).
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The log files for version 3.x are under
%LocalAppData%\SafeExamBrowser\Logs. In the client logfile for that session, you should find the reason why the lock screen was activated (probably an attempt to switch the active Windows user).