We have this every now and then too, but it's never consistent. A quick and easy mix is replacing the cabin air filter as a first remedy, as we've never had the symptoms with a newer filter. I believe the Pacifica is more sensitive to dirty filters than most other cars, but I can't wrap my brain around why or how.
If you do replace the cabin air filter, you can do it yourself, but buy it from the dealer or search the forum for a recommendation of a good web store. I only say this because at least where I am, the local and national parts stores (even the oil change places) think they have filters for the Pacifica, but in reality they are for older Chrysler vans or some other fit entirely.You need OEM on this one.
2017 Pacifica Touring L (gas) w/tow. April 2016 build.