If you notice when buffering/importing a transport that the tp command or STMS clocks for an extraordinary long time pull up the STMS logs and see if you can diagnose the problem from information there. Do the following:
Run TCode STMS
Double-click the transport queue you are troubleshooting
Once you are in the queue click on the Goto Menu and then ‘tp System Log’
See if you see several entries indicating that the trans/tmp directory is already in use (as shown below). This indicates that the transport process is hung in an endless loop
To fix this log into all of the application servers pertaining to the environment, kill all tp.exes that are presently running and then kill the temp file listed in the system log. Now you should be able to restart the tp command or use STMS and buffer/import as needed.