RC input missing after reboot

Hi all,
I am dealing with a strange problem right now:
I am setting up my copter with an R-10X reciever and a cube orange as FC. I got Telemetry working to my X21 and now working on the configuration of the FC.
My problems arise when I am starting to set the rcmap using the remote callibration tool from QGC. After finishing it, I get the message that a reboot is required for rcmap_roll to be applied. So I first did a softreboot via the software and a hard reboot by disconnecting the USB connection.
After that, there seems to be no signal whatsoever on the mapped RC channels. If I change the mapping, (on the remote or via rcmap_X) they come up again.
HAs someone expirienced something like that, or has an idea where to start troubleshooting?

Best, Andre