Tacho Rev Counter Intermittent Fault

My 2015 T100 has an intermittent fault with the rev counter. The needle briefly goes up to maximum revs and all the display lights flash on then off. It seems to be in particular when accelerating from low revs. I have been using the bike in very heavy rain so I have checked all the connection blocks and wires and everything is dry and appears OK. The bike has done 36000 miles so I can expect some faults now and again but this one has me puzzled.
Any ideas
David