Rear brake doesn’t grip/slips through and doesn’t stop the bike sharp or at all

I cleaned my bike about a month ago and since then I tried to fix both of my brakes.

I have hydraulic disk brakes (Tektro Auriga). After I replaced my pads, I was bedding them for over three days of consistent biking and braking on low and then high speeds, but it didn’t work. I bled my bike more than five times, and it didn’t help. I sanded those pads with 200 grid sandpaper and rubbed them with isopropyl alcohol. It fixed two of my pads – I guess because the front brake works fine (70-90% of the strength it used to provide), however, the rear ones don’t.

The brake feels sharp, not spongy or anything (I bled it twice specifically), but it feels like it’s contaminated with oil because when I brake, no matter hard or not, the wheel slides through the brake pads and stops very slowly. In rare cases, after 20-ish minutes of active braking (bedding in-like process), it starts squealing and bites just a tiny bit more, however, the very next day it appears from the very start e.g. close to no grip.

The only thing I haven’t don’t yet – burning or baking the pads.

BTW, I ordered new pads, but I still want to investigate why this occurred and how to fix it, because the pads which are used right now are two weeks old.