Tell me if I’m understanding the issue correctly…
There’s multiple Plugable USB to Serial cables and when they are connected and disconnected they get arbitrary COM ports every time, so the same cable won’t get the same COM assignment twice in a row.
Is that correct?
To isolate what’s happening it would be good to set a base line of expectations. Try having them use just one cable and then after a fresh reboot connect it and see what the COM port is. Then disconnect it and reconnect and see if it get the same assignment.
Next try connecting it into a different port. Does Windows still recognize that it’s the same cable?
I think the issue may have to do with Windows reserving COM ports that have previously been assigned and for some reason not recognizing that a particular cable was previously seen and assigned.
Once you define what the behavior is of one cable regarding same USB port, different USB port, try adding another cable and see if Windows behaves as expected.
I hope his helps!