Are you using a USBG to DB25 Female adapter?
https://www.youtube.com/watch?v=PaPDv4EDxVM
Note: This is a non-Microsoft website. The page appears to be providing accurate, safe information. Watch out for ads on the site that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it.
This was used with Citrix:
net use com7 /delete
net use \client\com1 /delete
net use com7: \client\com1
In addition the following Citrix Policies were enabled.
User > ICA > Ports > Auto Connect Client COM Ports
Client Com Port redirection was not used.
The connection was via ICA not RDP