Sometimes the end session by AX administrator or SQL can result into slow response from AOS from AX Client used by the end-user.
The sessions of the same user with Ending - Blocked status are actual causing slow response due to deadlocks in SQL queries.
The solution can be deleting the same user from SYSCLIENTSESSIONS table from AX transactional database.
delete FROM [SYSCLIENTSESSIONS]
where userid = '<userid>'
and status = 3 -- means the sessions which are blocked.
where userid = '<userid>'
and status = 3 -- means the sessions which are blocked.
Then refreshing the online user session form in AX 2012 - System Admin module will also show the sessions wiped out which were blocked earlier. The end-user will not face the issue of hanging or slow performance afterwards.