Diagnosis
The turn signal control module has likely crashed. It's a separate circuit from the main dashboard. A software glitch causes it to freeze.
How to Fix It
Perform a hard reset. Turn the scooter off. Press and hold the power button and the brake lever simultaneously for 10 seconds. The dashboard will cycle. Release the buttons. Turn it on normally. Check the signals. This reboots all subsystems.
If That Didn't Work
Check the physical connectors. Remove the four screws on the dashboard cover. Gently unplug and replug the two wire connectors going to the turn signal light bars. Ensure they are seated firmly.
Heads Up
When the cover is off, do not touch any circuit boards directly. Static discharge can damage them. Handle connectors by their plastic housings only.