If your blaster didn’t clean the metal after blasting and before shooting the epoxy, dust would do that. Normally you can shoot primer after blasting (and after cleaning) as blasting gives the metal excellent “tooth”.
You should take it back down to bare metal and CLEAN.

Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.