chemical reactions between glue, lume, dial base material and paint/clear coat will be the cause. Without long term research and trial and error things like that happen - same with some early rolex models that are so beloved nowadays because of the chemical reactions that are called patina...
What a pity... I feel sorry for the lucky ones that got one but are disappointed by JF like this... Maybe there will be a compromise in the future... Never seen such a thing on a JF ROO... (except some Safari dials where the brown lume color was leaking onto the beige/cream white dial)