A loose connection means higher electrical resistance, which leads to heat, which increases the resistance, which increases the heat, etc.
Not many folks think about that. It applies also to your wall outlets, extension cords, multi-outlet strips, etc. Any connection that's not a good, tight contact can start heating up. Eventually the connectors become brittle and won't even "conform" well to the mating connector. But you know that already...

I'm curious what brand fan / filter combo you've got. The combo sounds like a Can Fan setup but their workmanship is excellent. You should not see what you've described with their products, IMO.

Maybe some pics or a diagram of how exactly your airflow's routed, and where your components are, would shed some light. Some folks just have a scrubber sitting in the room doing its thing, separate from the ventilation system. If you pump air out of a room like that before the scrubber can clean it, it'll smell.

Others pull the air out of the grow room through the filter. Is this how you've got it arranged? I'm confused about the "other rooms" and where the fan is. You pushin' or pullin'?
Regards, Hermie.

And KW420 is right. Humidity can affect a carbon filter.