You may be unintentionally trying to use one port on the 991 for both applications and getting a port conflict. The FT-991A has two independent ports on the back, one USB and the other serial. Either or both can be used for CAT. They have separate port numbers. You might try using both at the same time with different applications on each one. For example, JS8 into one (I am not familiar with JS8), and fldigi with flrig for rig control into the other.
I'm guessing that your laptop does not have a serial port. If it doesn't, you will need a USB/serial port adapter to use the serial port on the 991.
An alternative might be to use a virtual port splitter, and run everything through either the USB or the serial port on the 991.
These methods will keep everything in sync, including on the same freq. That may or may not be what you want.
