Hi,
Of course you can't share a COM port with several applications at once unless you use a virtual COM port. I suggest you install and use OmniRig v1 from
www.dxatlas.com. It's a free program supported either by Swisslog and WSJT-X. You only have to configure your radio and COM port in OmniRig as Rig1 then select OmniRig in Swisslog and WSJT-X. You won't have any conflicts because OmnIrig will handle the COM port and will send all CAT info internally to the supported applications.
Best 73