Soft pedal with not much brake could well be just the pads deglazing.
If you drive gentle most of the time, the pads can glaze, more of a problem with some more than others, they could actually have overhetaed very easily this way, but now cooled will be fine after a few miles, the resin that bonds the mix together comes to the surface when they glaze, but a good roasting to the point of fade gets rid of it.
I had this problem always with the DS Ferrodo pads I used to use, just got hot enough to bite decently then 5 mins later they fade.
It would not hurt to examine the pads though as the material may have started to come away from the backing metal, small cracks are ok but not chuncks missing.
Could have been a few sticky pistons helping to warm pads up as well.
I too would have said fluid except you have changed it, was the fluid new ?
Any stored fluid WILL absorb water even if still sealed, and it has a shelf life, that is why I no longer buy 1 gallon at a time but as needed, so always fresh.
tabetha