I've had every brand of epoxy that I know of, Anchor, devcon, tower, GP, BSI, HK, you name it...never had an issue in those short time spans you have described. Always over at least a year! I wonder, what temperature(s) are you storing these adhesives? I know you said in the house, but that's it. I just ordered a 9 ounce set of tower 6 minute and 30 minute epoxies from Tower, so, for all I know maybe they have changed the formula, in which case I will be upset as well...