Hello @hseidel re-reading FAQ Q36 I think the compatibility is about GPIO compatibility (electrically) and not about pin length. BTW: I double checked the length of various modules I have (Battery, Proto, M5GO, M5GO2) and afaikt they all have the same length of pins. Some of them have been bought before M5Core2 came out. Maybe they all have the longer pins already and I do not have modules with shorter pins? Anyways, I do not have a connectivity issue when stacking any of them to my M5Core2, but yes, the connection feels a little weak sometimes. Thanks Felix

Since this concerns many modules a photo of the necessary modification would be helpful.