Does vegetable soup made with chicken stock last longer if the stock was made fresh vs from a stock cube?

It's probably OK but there are a lot of variables here so from where I sit, it's difficult to be certain. Cooking will kill most bacteria. If the soup went from the pot, hot, to the container and capped immediately, the risk of airborne bacteria getting in is reduced. It takes more than a couple bacteria to get you sick but when conditions are right, bacteria multiply exponentially in a short period of time. If the container was at 72F, that's better than if it was at 90F...as if it was outside in the sun.

You can give it a sniff to check if it smells OK. Reheating to a boil will kill most bacteria, but depending on the specific bacteria, not all. What's more, certain bacteria leave behind toxins that are not easily destroyed. If you have a pressure cooker, that's the best way to kill whatever bacteria might be in there. You would need to keep it in the cooker for a period of time...30 minutes perhaps. Seems like a lot of trouble to go to.

Dry bouillon cubes should not have any bacteria...assuming a clean manufacturing plant. Same goes if you used dehydrated chicken. It's more likely bacteria got in if fresh uncooked chicken was used. Unwashed hands, contaminated utensils, used hand towels, unclean work area...all that stuff comes into play. You probably already know about cross contamination.

But here's the thing? Why risk it? Salmonella will not likely kill you but your stomach will be churning and you'll be spending some time in the bathroom. There are other bad actors out there and they are worse than Mr. Sal Minella... Staphlococcus, E. Coli, Botulinum.

My answer is, to be safe, toss it.