A longshot as an explanation but I noticed that on "old" Fuj paper boxes such as MP and CA the boxes were all "raw" uncovered cardboard unlike Kodak and Ilford which has thicker cardboard which is covered by what appears to be water resistant smooth and shiny paper.

In a fridge any water droplets or humidity will stay on the raw cardboard and maybe form mold. Water droplets cannot penetrate the covers on Kodak and Ilford boxes or indeed most other makers' boxes

However Fuji was the odd one out with thinner and uncovered cardboard.

pentaxuser