Tested on Joomla 3.9.27, PHP 7.4, Apache 2.4 and CB latest 2.6.0
Made clean default installation of Joomla and CB to avoid any conflicts with any other Joomla extensions.
But anyway - comprofiler_sessions table is empty, no records about user's sessions.
Why ?
What specific setting should be enabled and where ?
If nothing "special" required - than it seems to be a bug,
Please, comment
Regards,