2021 XC40 here. About one month ago when we had rain here in L.A., we also noticed water build up on the passenger floor mat and took it to the dealer. They said it was a clog that needed to be cleared and it was resolved.
The other day, we took it to a car wash, and this time we noticed water build-up on the floor mats on both the passenger side and driver side. Much more on the passenger side.
We proceeded to drive to our destination and the air cabin fan would not blow into the cabin. We could hear the fan, much more loudly and noisier, but got no air out of the vents. We tried to reboot the infotainment (press and hold the home button on the center display for 20 seconds) but the fan would not blow.
3 hours later after getting into the car, the fan was working again. We think it got waterlogged and needed to dry out. This seems so dangerous and unacceptable.
We also have issues with the infotainment screen not displaying the correct XM radio station that is playing. But I guess that is for a different forum :-/