Odds on (as has been said) that the slider pins are not working as intended.
An easy fix if you have the tools etc but as you paid a “dealer” get them to sort it.
A caliper in most cars has a piston only on one side, so that is doing the work to squeeze the pads onto the disc, it does though rely on the the sliders to exert the same squeeze onto the other side.
Bit of friction, not sliding as they should, contamination, no correct grease etc etc & etc you have what the pictures tell us.