Typically caused by a low or bad battery connection or positive cable shorted to frame so check for that.
Or starting (or bump starting ) the bike with a really low battery (8 volts) and letting the generator bring the battery back up to 12.6 + volts
If you have anything added or altered other than 100% original wiring it could be a issue
If you can trade the meter unit with another Z' you will know if it's the meter unit or problem with the bike. Maybe unplug the connection under the meter unit and plug back in (bad connection?)
if Red battery light is on while engine is running, Check for battery for 12.6 volts
If the CEL is showing while engine is running check for the code
Check the speed sensor
Also can try a ECU reset but don't think I've seen anything work before and everyone had to replace the meter .