When I did mine - and I removed all the brake lines in the engine bay to respray it, I had issues the first time bleeding.
I was told this solution and it worked for me -
Bleed the brakes until as you say the pedal goes hard when the car is off
Wedge a piece of wood from the drivers seat (put a bit of card on the seat to protect it) to the brake pedal so it is held hard down.
Leave overnight then bleed again.
Repeat the above, I did it for 2 nights and the brakes bled out and are fine - not sure if it actually works or it's just a lot bleeding that really solved it
Just thought I'd throw it in