A mismatch in your OpenTX versions and/or the SD files? In Companion, go to "Help" and "About" to find out what version it is. On your TX, go into the bootloader (hold the two trim levers, and power on), and verify the version there, listed on the bottom of the screen.
Companion uses the "SD card" files that are stored somewhere on your computer. (In Companion, got to "Settings", then "Settings" again. Look for the entry for "SD Structure Path" for where the files are on your computer).
The TX, of course, uses the files that are on the actual SD card.
TX and Companion should be on the same version. And the two locations for the SD card files should each have the files for that same version.
A few like to change the "SD Structure Path" to go directly to the SD card in the transmitter, in order to only have one location to keep track of the files. But that means you have to hitch up the transmitter to the computer if you want to have full function in Companion. It is kind of a pain to update two locations when changing version software for OpenTX. There is a "synch" function in Companion to coordinate changes from the files on the computer to the files on the SD card....but I tend not to trust processes like that - too easy to do it wrong, and overwrite/loose files, so I don't use it very often.