Honda Pioneer 1000 2017 Owner's Manual page 268

If the driver's side seat belt is not latched properly, the maximum
vehicle speed will be limited to no more than 15 mph (24 km/h) by
the seat belt interlock system (page 67).
Also the seat belt indicator and speedometer digits blink.
Make sure that the driver's side seat belt is latched properly.
If the problem persists, see your dealer.