Diagnosis
You likely have a filter designed for the original MA-40, not the V2.0 model. The frames are slightly different. An incompatible filter will not seat correctly against the internal gaskets.
How to Fix It
Verify the filter model number. The correct replacement for the Medify MA-40 V2.0 is the 'Medify Air Replacement HEPA Filter for MA-40 V2.0'. The filter should have a rigid, blue polypropylene frame with a precise rectangular shape.
If That Didn't Work
Remove the filter and inspect the internal sealing gaskets inside the unit. Ensure the black foam gaskets are present, intact, and not dislodged. A missing gasket will cause a poor seal and allow air bypass.
Heads Up
Using an improperly seated filter drastically reduces efficiency and can cause increased noise. Air will take the path of least resistance, bypassing the HEPA media entirely. Always purchase filters from Medify or authorized retailers specifying the V2.0.