Random Vendor port when no Vendor port is specified ?

"The SERVER port is typically between 27000 and 27009, and the VENDOR port number is typically between 1700 and 8000"

From: https://knowledge.safe.com/articles/19460/specify-port-numbers-used-by-flexlm.html

I'm guessing that means that FlexLM will use the first port that's available, but I'm not sure, it could also well be that there is some random selection involved. If you have to open a specific port in your firewall I'd recommend specifying the port numbers, as described in the link above.

This goes beyond the scope of FME, but here are some tips on how to check if a port is open (on Windows): https://stackoverflow.com/a/273188