Wow- 3 different codes in one trip? That makes for quite a day!!
Code 21 - accelerator fault safety lock out inspect accelerator resistance and wiring
Code 16 - voltage high electrical fault verify voltage >86vdc, if higher, run lights to reduce
Code 77 - vehicle over speed error inspect motor controller
Weird… All not really related. I say there is something going on inside your controller. Check the main plug first. Look for dirt/corrosion/water where it shouldn’t be.
Where are you located? Has it rained lately? Wave you washed your car?
If it continues, remove the motor controller and take it apart. Look for water ingress, corrosion, maybe bits of something bumping around in there.