So, after 2h of testing debugging and modifying the Marcos I found the issue.
Totally cracy combination:
I use your Xbox plugin, Eric and I recently experimenting with an A-axis. I put the A Axis on the same joystick as the Z-axis. I activated to move 2 axis at once. The A axis is much slower but the plugin can overwrite the maximum speed of the A axis. When this happens the controller goes into this error mode with slow G0 motion. This is only limit in G90 mode in G91 the G0 speed is ok.
UCCNC then needs to be closed an need to be stay closed for ~30 seconds. Afterwards the controller recovers again.
Eric it would be good to have again the 0-100% speed settings of all axsis with the Joystick. This would prevent such a failure.
And thanks for helping!
BR
Michael