Yo Jess, keep in mind, that coolant cap is designed to leak off at 17.6 psi (that is 1.2 bars of pressure, and is printed on the top of the cap). Our caps can vary several psi in either direction without causing a problem.
It could be that the cap was just doing it's job, and purging excess pressure. That would also explain the squishy feel of the hose, from the vacuum created as the system cools down after the loss of coolant, and possible loss of bleed from the pinched-off hose, and it then gets worse, etc.
So, I just HAVE to ask --- have you cleaned that "Majestic Mud" from between the radiator fins? you know, that sticky red PA stuff from the group ride? LOL......just kidding, but fishing too.