CubeCell HTCC-AB02A and moisture?

I have some problems with HTCC-AB02A nodes, all in IP65 case outdoors.
I use a total of 12 sensors.
Some of them stopped working after some time. I then checked them in the field and noticed some condensation inside the case, but not too heavy. After opening the case, letting the node in the sun for say half an hour, most of them started to work again.
At the moment I suspect that the nodes stop working because of condensation water inside the cases.
As a workaround I tried to add some Isolation Spray on the PCB, which seems to help.
Has anyone encountered the same problem or has some hints what might help?

Electronic resin but your PCB will be no accessible anymore.