I have had a few batches of what seemed like it was going to be my best batch ever go sour - and I think its because I waited over night to pitch yeast.
It sounds like some portion of your equipment didn't get as clean as you thought it did. If you take fresh, cooled, wort and put it in a sanitized sealed container it should take +3 days for properly boiled wort handled by well sanitized equipment to start fermenting.
Shame your batches went sour. Did you continue any as sour experiements?
I recently listened to a podcast where they talked about how a lethal bacteria (botulism maybe?) can easily take root in no chill wort cubes.
That certainly sounds like botulism.
I haven't done any no chill experiments but if I were doing long term storage I would follow the procedure outlined in my link: Bleach the 'cube for 20 min, probably use hot water and a full 5G of bleach solution followed by 3x 1Q DI water rinse and sanitize as usual.
Since you're using tap/DI water there shouldn't be any spores in that. I suppose there could be some on the grain. If you store it for months though and have any infection there should be bulging in the packaging to tip you off.
1°:Haphazard cyser, Graham's English Cider, Cider; Conditioning: Banana wine, Cider, Orange/Clover blossom mead, Cyser, JAOM, In like a Lion RIS ; Drinking: In like a Lion RIS; Mango Melomel