I doubt if reoccurring mold is just growing on it's own. A leak or rot behind the spot is the probable cause, you're just seeing the result. I think you're going to have to cut into the wall or ceiling to find out what's causing the issue. To continue to just clean the surface won't cure the problem, it's going to take more aggressive probing. A mold issue can cause serious sickness, as I'm sure you know.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI