Manual mesh bed leveling issue?

Hi!
Using an Ender 3 with a warped bed, so I got the TH3D firmware to get mesh bed leveling.

I first do corner leveling, test print, repeat until good.
Then I do 5x5 mesh level procedure, store the data, check with M420 V1.
Enable bed leveling form the LCD.
Start corner leveling and my corners are off (I don't touch the adjustment knobs)?
Disable bed leveling.
Enter corner leveling, my corners are level again?

With bed leveling my nozzle gets to high and all prints fail.

I've redone the the procedure multiple times, with the same results.
I check the completed mesh after every run and I get the same geometry every time.

I guess I'm doing something wrong, but have no clue what.