My observation regarding wing skin separating from the rips is:

Even if the preparation and gluing is done according to specs, under certain flight conditions, like hitting a short cycle powerful vertical gust ( thermal) at high speed (100kt) the lower skin on the negative rebound will compress. Because the FX 67-15 is a relative flat airfoil on the bottom it may pop. The top skin is spared because of its pronounced curve. Also sanding flat spots can start the problem.

I repaired the separation by drilling 1/8" holes dead centre on the rips, about 1" a part. I went into the foam about ¼". I also used a Dremle tool (I used a small ball bur) that fit easily through the 1/8" hole to make a bit of a slot in the foam( parallel to the rips) A syringe was used to squeeze the epoxy in. If the epoxy pooled on top of the hole and did not drained away, that would be a good sign. If it did drain I would use a carbosyl/epoxy mix and push it in with a spatula. The repair relies on mechanical bound only, like an epoxy rivet.