DIAGNOSIS This is a software sensitivity issue. The scooter interprets a steady, light throttle pull as an intentional cruise control activation command.
FIX Disable cruise control in the app. Open the Segway/Ninebot app. Go to your scooter settings. Find "Cruise Control" and toggle it off. This is the only sure fix.
IF THAT DIDN'T WORK If it still happens with the setting off, your throttle may be faulty. It could be sticking slightly or have a bad sensor. This requires a throttle assembly replacement.
HEADS UP Do not ignore this. Unexpected cruise control activation is a safety hazard. It can cause you to lose control if you aren't expecting maintained speed. Disable it until resolved.