[Advanced Design]

Sounds like front brakes became over heated and started experiencing brake fade. Same as doing a number of high speed stops and the brakes become less effective. The pads are likely glazed and don't work as well now. If mine, I would replace the pads, look the rotor surface over for pitting / grooves, measure for parallel, bleed to balance the warning switch and evaluate. And may be a bad master too.

Also check the front hoses for collapse. If you weren't using the brakes much and they got hot, a hose internal collapse can keep the caliper applied overheating the brakes.