Factors such as a forward-looking riding style, good terrain conditions (e.g. gentle inclines and flat, asphalted surfaces), body weight, and the outside temperature can have different effects on the performance of your Moovis.
Although your Moovi isn't currently performing at its desired maximum, it's likely fine. It's possible that your Moovi is incorrectly configured, which can be resolved by adjusting the "P8" parameter:
To enter the menu, hold down both buttons on the display for about 3 seconds.
Once in the menu, briefly press the top button until P8 appears. A number will now appear, which should be set to 100.
To exit the menu at the end, hold both buttons down for 3 seconds.