Someones metallurgy or corrosion control needs revision.
I would bet it was a revision that caused it.
Someone (EPA?) probably declared the standard (many decades) acid etch, alodine and epoxy primer process for aluminum to be “non-green”.
I'm sure these F-22 are new enough to get green credentials, it's just a pity that the green materials don't work as well.
Heck, the Navy has parked their aluminum planes on carriers surrounded by lots of salt air - they don't get corroded in less than 5 years.