Found out what it is. Something really stupid.
Before I had a TNC-PI. That TNC-PI modem just starts sending as sook as it gets data. The Kenwood on the other hand checks for a signal on the waves. If any; no packet transmission. And apparently this controlled by the squelch. I had the squelch set to "always listen" but then the radio things there's ...
This might be caused by RFI.
Perhaps RF might be getting into the other equipment —especially the Raspberry Pi— and causing this problem.
Does it help if you turn the Kenwood's power down to 5 watts, or better yet replacing the antenna with a dummy load?
I guess F, VFO would do it since that copies the memory to the VFO, and the name doesn't appear in VFO mode. Given the small number of buttons on this radio, there's probably not a better way to do it.