Ec25

If it hasn't snapped change it anyway as it is probably worn (belts should be replaced every 6 months on clutchless models, clutch model belts aren't a customer replacable item.)

While you have it apart check your brushbar is spinning freely.
If it isn't spinning cut any hair off around the bristles, then take the endcaps off and clear any dust and hair in the ends. Spray some WD 40 in the ends for good measure and put it back together.
If it still doesn't spin freely then I recommend replacing your brushbar.

Have a look at the soleplate and the housing around were the belt and brush sits, is there any bent plastic, black marks were the belt has been rubbing or anything obstructing the brush like dirt or hairgrips?

The black marks were the belt has been rubbing may not be a problem if you know your belt hasn't been changed for a while (a year or more) once the new belt goes on the belt will not slip and slide as much.

Once you have replaced your belt, brushbar or both put it back together and it should be back in working order