Rust coming through new epoxy - help

[ItWillBeSlow]

A couple months ago I was spot blasting minor rust pits off the exterior cab while getting the cab ready for primer.

I blew a small pinhole in the metal, just behind the door in the B pillar area. This location is where the interior B pillar and exterior cab sheet metal are overlapped, and there is some seamsiller (or something) in the joint.

I had to notch the interior B pillar metal lip, peel it back, and place some copper here to get the exterior hole filled without constantly blowing holes. It was a mediocre repair but seemed to get the job done. I tapped the notched metal back down and left as-is since its an invisible area.

I noticed today I had rust bubbling under my 2 month old epoxy. The cab has never left my garage and Im surprised and concerned this happened, and so quickly. I obviously did not remove all the rust behind this lip since it is borderline impossible based off the way the cab is constructed.

I scraped the rust bubbles with a screw driver, so that's why they look the way they do. I also have a single small bubble just above my cab corner seam.

This is epoxy over metal, no bodywork or filler hence the ugly seams.

How do I fix this?