The problem areas seem to
: be independent of the age of the epoxy, ie., some areas where the epoxy
: was only a few days old were fine, and other areas that were months old
: were gooey.

Hi Bob,

I’m sorry you are having such difficulties. I used Minwax Helmsman urethane CLEAR varnish over non blush Raka epoxy 127/350 and everything went fine. The drying time was about 4 hours for the Helmsman urethane varnish. You wouldn’t have a blush problem since you sanded before varnishing. There weren’t any solids to be mixed up in what I used. I think I remember seeing a Minwax Helmsman urethane semigloss that would have had some solids in it to be mixed up good. But that doesn’t answer the spotting drying your having. Is their anyway any waxes could have been under you epoxy in it or on top of it somehow?
If I got this right that the old epoxy was the area's that the varnish didn't dry on, then iy sounds like something has been absorbed into the old epoxy. Strange.
John