If you didn't have the meter, is this something you would notice? Could your meter be defective? I worked at a semiconductor facility for years, and we had one hand held meter that ended up being faulty and this meter cost over $5,000.. Also, the vent for the canister is in the rear outside of the car.
Have you replaced the cabin filter? Do you always run the climate control on auto? Is the system set on recirc when it happens, or is that turned off?
What do you have your meter set up to measure?
Typically what happens is I'm in my car and my eyes start burning, I look down and the levels are maxed out. I have also brought the meter to many places and every time it has shown high levels, there was a valid reason (fresh paint, baking, cooking, gas/wood heating, etc.)
I just bought another cheaper meter and I'll do more tests.
I don't think it has to do with the cabin filter. It can happen with the heat on or off, recirc on or off. The levels are so high that it just goes through the cabin no matter what. But other times it's 100% fine like no problems in my commute home tonight.
I just have my meter in the center console. If I move it around the cabin, nothing happens, it stays maxed out. If I take it outside, it goes back to ~0 in a few seconds.
Reading my logs, it ALWAYS happens within 4 miles into a drive. Either right when I'm leaving a place, or soon after entering the highway. It has happened after a cold start, after a 2 hour break, or after a 5 minutes break.