I switched the film to the vapor pressure mode and the predominant drive into the layers that are gaining moisture seems to be from the inside of the wall. In the animation, does the length of the arrow show magnitude of the drive or the depth in the actual material(s)? Does the arrow have to fully cross a layer for the vapor drive to be going through a material and into the next layer?
The length of the arrow is scaled to it's maximum - either global or per time step (configurable on tab "/edit/properties/moisture/water_content"). Hovering the mouse over (stop film at desired time step) opens a hint-window showing its actual magnitude.
I'm not really sure what to look for/how to read what the pressure is doing.
Diffusive driving potential is the Vapour Pressure - which could be written as a function of R.H. and Temperature (R.H.=vp/vpsat(T) -> vp=R.H.*vpsat(T)).
Because of the "convenient" ambient tempurature at the inner side (the pool area) the vapour pressure gradient will force the diffusive flow towards the inside during a significant period of the year. Just a guess