Here’s what happened:
I had 2 encoders plug in adjacent digital ports. (Using RobotC)
When configured like this a simple program such turning the motors on then off when a bumper is pushed will freeze leaving the motors running and the remote screen gives up a “Failure to read brick status” message.
Turning the controller off and then on to reboot the program will find the motors still running.
Trying to re-download the program fails.
Then the VexNet link fails either wifi or tethered (tried to relink via the tether).
My Joystick is sitting read with the Robot LED blinking slow green and the controller Game LED blinking fast green and I am unable to access the controller in any way.
This happened once before and after leaving it alone for a couple of days I turn the units on to find the link established.
I experimented and found that the adjacent encoders were causing (or one of the causes) the problem.
Batteries are good. Five years with Vex. An experienced programmer. But stuck on this one & left with inoperable equipment.