Hello,
I would try the most obvious 1st, replace the appropriate fuse/fuses, may be cracked & only working intermittently, unlikely I know but possible

, then I would check the connection behind the Speedo, unplug & replug, see if any gung in there, check for any loose wires,
Beyond that I’m not to sure, could be dry joint in printed circuit board of the binnacle??
Good luck mate
Martin