White furry mold on hive wall

I found water and white furry mold on the bottom of one the brood boxes of my weaker hives (split from stronger hive still no queen). The frames look fine. I am going to put them in a new box tomorrow and dry out their box and run a torch on the inside to kill any spores etc. unfortunately I don’t have any photos. First time to see this. Recently started painting my boxes and was thinking with the paint the hives don’t breath as well…anyone ever had this problem? Btw in Okinawa Japan so about 17 Celsius and kinda rainy lately