[Mondaveo]

Is this the standard gauge cluster, or Covers+ display? Are we taking the whole display goes blank (including odometer and trip computer) or just the fuel gauge and consumption readouts?

Best first suggestion when you don't have a clue is to get an OBD scanner and FORScan to check for any DTCs in the various computer modules. You'll possibly see one that says something like "failure to communicate with instrument cluster" or similar. We can then try to troubleshoot from there.
Other suggestion is to check your fuses - no inkling it could cause this kind of issue, but you never know and it's easy to do.

Alternatively you can try sourcing a replacement cluster from a wrecker and swap them around to see what result you get - seems extreme but it may be the easiest way depending on what resources you have available.

Hope one of those helps...