Burnt Mauch Power Module

I’m using a Mauch power cube V2
The specific power cube I’m using has been kept in storage for the past 3-4 years in its original package.
During ground tests, connected to a 6cell LiPo battery for 15 minutes, one of the capacitors burst into flames ( pic attached ).
Does anyone have any idea what could have caused this? I have a few other Cubes that were in storage and I want to make sure it wont happen to all of them