Sounds like an "inproper use of equipment"..
Check to see if the weatherproof fixture is listed for use inside, in a high ambient temperature location.
It probably isn't listed by the mfg for use in a kitchen with high ambient temperatures.
Heat is the main killer of ballasts. The "old" ones were/are a lot larger in size, and can handle heat for longer periods, but they also are not listed for high ambient temperatures.