Hi,
1.How did you start the remote connection from the client to server 2012? What is the OS of client you are using?
For normal remote connection starting via mstsc command on Windows 10 client, the port redirection is accomplished by enabling port redirection policy on target server and then check the port redirection option in mstsc.
Windows Components\Terminal Services\Terminal Server\Device and Resource Redirection
"Do not allow COM port redirection"
"Do not allow drive redirection"
2.Per further checking, one user confirmed that you can not delete the ports prior to redirecting them.
https://social.technet.microsoft.com/Forums/en-US/9debb32c-f8d7-43d9-9892-9ce6ec8f7f51/communication-port-redirection?forum=winserverTS
3.Not sure if you are using citrix servers, but kindly check if the guidance below could assist.
COM Port Redirection: How to map a client COM port to a server COM port
https://support.citrix.com/article/CTX232422
Please note: Information posted in the given link is hosted by a third party. Microsoft does not guarantee the accuracy and effectiveness of information.
Hope this helps and please help to accept as Answer if the response is useful.
Thanks,
Jenny