That’s good troubleshooting. Let’s further divide and test.
- confirm configuration - please peek inside the Digirig to confirm it is set for RS-232. More info here.
- confirm that Digirig’s serial port is working correctly with the loopback test.
- I’m not aware of this issue with TS-450S, but there was a combination of factors affecting another Kenwood that caused CAT to not work reliably. If everything else checks out, this is still a possibility.