We need some more information to help you out with this problem. It would be best to open a ticket with us at https://support.wavelink.com/
Some items we would like to look at are
An export of the device settings, from the working and problematic device. (the configuration utility has an option to import/export your settings). Is it possible that the MC9190 has some keymacros in the configuration and those need to be added into the Falcon?
Another helpful item would be a log from the working and problematic devices. This way we can see what is being sent from the working device when you press the key and measure it against what the problematic unit is sending.
To enable logging see