Not sure about yours, but many extractor (vent) fans will just suck the air over a very loose filter and throw it back into the room. Many in the US are part of the over stove microwave and rarely vent at more than 250cfm (~7 m3/min) where specific vent fans that go outside can move upwards of 700-800cfm (20m3/min).

Author here. I really want to figure out if my extractor fan is actually doing anything good.