Seam Sealer Bubbles

Have noticed recently bubbles forming in the seam sealer in the bottom and sides of a couple of my doors and in front hood. Never saw them before so it must be a recent thing. Was worried it was rust forming in the pinch welds. So I sliced one open and to my relief not a spot of rust, just an air bubble in the sealer under the paint. Anyone else see this before.

Truck is a garage queen that is not driven in snow, although I do drive it all year just not when roads are wet with salt. Garage is cool and dry with a dehumidifier running in summer. So couldnt imagine rust forming in doors. Frame is rustfree from yearly oil sprays.

 

Looks like spot to me