Strange control panel (white instead of black & no work)

I use a VM201 since more one year and no major problems on it except one strange issue :
sometimes, the connection to the card doesn’t start on the right way : the panel font appears white instead of black and no function is reachable. The problem disappear after a certain time but during it, the card is impossible to control. Is anyone facing with such a problem ?
What is the solution ?
Regards,
Philippe

Sorry, this behavior has not been reported before.
Did you try resetting the board (i.e. remove power & network, wait a while, re-apply power & network)?