Some possibilities come to mind:

1. A caliper is stuck or sticky, increasing temperatures on that pad & causing it to glaze over (hard surface), therefore gaining a slicker surface, therefore needing more pressure to stop. I have also done this without a sticking caliper in my old motorhome by using too much braking in the mountains & frying the pads (& the calipers, boiling the fluid, etc). I have pulled pads that are so glazed & hard they ring like bells if you tap the pad surface with a screwdriver.

2. Some pads (I seem to dimly remember) have 2 compounds on the friction material: mostly softer for good braking, and a thin layer of harder stuff for bad braking to indicate a pad change is called for -- before running out of pad & scoring the rotor.