Two days ago we re-caulked our tub using DAP Kwik Seal Ultra and left it undisturbed until today. Unfortunately it developed these brownish yellow spots and I am unsure why. I haven't been able to find anything online that is similar to this situation as most articles discuss caulk that has rotted or molded over longer periods.
Despite caulking the entire tub at around the same time, the spots only appear on the seal on the outside of the tub, between the tub itself and the walls and ground. There is a fairly large gap between the tub and floor, and also between the tub and one wall, so backer rod and fairly thick lines of caulk was used in these parts.