Help: I've encountered an epoxy problem which I hope someone out there can help me with.

Glassed and epoxied the hull earlier this past year (spring & above freezing, but not too warm) When sanding out the edge last night, to apply the sealing tapes on the hull/deck joint, I encountered the top layer of epoxy on the hull acting like varnish which didn't get a good bond. Today I've scraped one half of the hull, with the problem consistent from end to end.

I'm using East System epoxy. I believe I got the 5:1 mix proportions correct based on the problem being on the entire hull. Epoxy was relatively new stock(at least to me) The outer layer, the last of the 3 coats, seems to flake off, leaving a smooth surface underneath.

Any suggestions as to cause, and whether another finish coat of epoxy should be added again, and with what surface prep.??

Thanks all for your help and suggestions.