I've seen that "A Test or Calibration is running..." hang on SA 5.3. What fixed it for me:

Disconnect machine + close SA completely.

Kill background services: stop SA Client/SA Communication Manager in Services (or end ServiceAdvisor* tasks in Task Manager).

Clear temp/session data: delete %ProgramData%\Service Advisor\* session folders and %ProgramData%\Service Advisor\Logs\* (keep backups if you want).

Reboot laptop, then connect to the original machine (the 450J), open Tests & Calibrations and explicitly hit Finish/Abort on any active job.

If it still sticks, remove the cached connection: Device Manager ? Network/COM entries used by SA ? uninstall (check "delete driver software" if applicable), then reinstall your adapter driver and reconnect.

Side note: I moved to Service Advisor 5.4 you can buy from here: (https://machinecatalogic.com/john-deere-service-advisor-5-3-construction/)
and haven't hit this issue since-5.4 cleaned up the stuck-session problem for me and works with Nexiq USB Link 3 as well as EDL.