Originally Posted by
alxsmlv
Ok, based on comments I believe the rotor is contaminated, I will have to clean them. I also didn't bed the front brake after the pads were changed which could contribute to the issue.
The rotor is 160mm Shimano Ultegra R8000 and the bike is Giant TCR.
I didn't bed in my brakes. They eventually bed in just with your normal riding. At least mine did. Took about 300 miles before they started stopping better than the rim brakes of my previous bikes. Over 5000 miles later I still haven't worn the pads down enough to replace. Mine are Ultegra BR-R8070 disc brakes with a rotor that looks similar to yours.
If you do try to bed in your brakes, next time you change the pads or rotor, then be certain you don't come to a full stop while you are braking hard to bed them in. Bed them in where you don't have to stop so you can let off the brakes and let them cool while moving.