Mazda CX-5 2018 Owner's Manual page 310

NOTE
If the vehicle speed decreases by about
•
15 km/h (9.4 mph) or more than the set
speed, the cruise control function may
be cancelled.
When the vehicle speed is less than 21
•
km/h (13 mph), the cruise control
function is cancelled. In this case, the
vehicle speed will not return to the
original set speed even if the vehicle is
accelerated to 25 km/h (16 mph) or
higher and the RES switch is pressed.
Reset the cruise control function.