Sportster front brakes go soft

2003 Sportster 883. I bled front brakes. They stay hard for 2 days then soften up.

I replaced the front master cylinder with a used one. I replaced the brake line. New crush washers. I also rebuilt the caliper with new pistons and seals.

Also what is weird is it won't reverse bleed. Fluid will not go into caliper bleed nipple.

I'm confused....

Thanks, Ken