you are probably correct on the hardener and temps. i think that was my second suggestion after old products shelf life.

with urethane products technically the catalyst is bad 30 days after it's opened.

old products can react in unusual ways. i have used 5 year old products without problems and used 30 day old ones and had problems. urethane products can react to high temps and humidity so proper solvents for the temp it's used in is important. sometimes the primer solvent or hardener solvents evaporate while sitting on the shelf if the lid isn't put on properly. if enough solvents evaporate you can over catalyze without knowing it.