The SHow REQuest output seems to say that the request number is 001,
so do Query REQuest 001 and see if that returns results, whereafter
you could try CANcel REQuest 001 and see if that works.

Also do Query PRocess F=D and Query SEssion F=D to see if any are
lingering on a mount request.  The Checkin that you cancelled is
probably the thing that had incited the mount, and you believe that
process is gone.  The circumstances suggest that the operation did not
complete either because of an absent tape or a tape drive problem,
where this is effectively an uncompleted hardware operation causing
the stuckee.  You probably know the volume name, so can conduct a
search for that, and reinstate it if absent.  Perform a check of your
drives, and perhaps use SHow LIBRary to look for anomalies.  Manually
satisfying the tape introduction or mount request may resolve it.
Definitely check back in your Activity Log in the time period
suggested by the elapsed time value for evidence of a problem.  If
nothing works, you'd have only the TSM restart recourse.

   Richard Sims