The clue is this -138 error in the Plex Media Server logs
[Transcoder] [tcp @ xxxxxxxxx] Connection to tcp://127.0.0.1:32400 failed: Error number -138 occurred
The movies libraries can be upgraded to the new in-line Movies Scanner and should therefore not cause an issue with the port usage for scanning
The TV Shows is still scanning in a separate process and so remains a problem
A curl update to be incorporated into Plex Media Server will reduce port usage by 66% whilst scanning which should help and will resolve the issue for some users. For others and until that fix is out, may need to split the TV Shows library and increase the dynamic ports and reduce time_wait