Warp is usually caused by thermal shock. Cold liquid into a very hot can cause it.
I just scrub my carbon steel pan out with hot water, but not when the pan is hot.
27 years ago my partner and I broke up and sold the house, so we each came into a bit of cash. She took the cookware and I took my prized Wusthof knives.
So I used some of the money to buy more than a few pieces of All Clad stainless cookware — discounted cosmetic seconds from Cookware and...
IMO, you are doing everything properly. And your skillet looks great.
I wouldn’t worry about the residue. Seasoning is polymerized fat so it will give that off.
I bought a lightly driven 2023 Audi Q5 and its warning features scare the shit out of me every day. I mean they are great but they are also loud and fussy. And a 300 page owners manual.
Still, I love the car and it’s advanced features.
But I’m not a fan of driverless vehicles.