The answer is simple...vacuums with filters allow air and anything finer than the size of the filter holes to pass through...if you hold a light over your bag and turn the vac on, you will see an explosion of fine dust coming from the bag...Vacs work on airflow, so the less air flowing through the bag, the less dirt you pick up...clogged bag = no airflow=no cleaning. Bagless vacs should have the filters cleaned after every use, and the canister emptied and washed. Buy a Rainbow to eliminate these problems.

Could be blocked check out the tubes where the dirt goes in