[PHM]

Are caliper pins sliding with no issue.

 

[PHM]

I will be bleeding out old DOT 3 fluid in rear pads tomorrow.

Are your caliper pins sliding freely.....

 

[PHM]

I did forget to remove the pins and relubricate.
I will attempt tomorrow.
But how would that cause brake pedal to be spongy first push but not second?

If the pins do not slide, the piston has to take all the slack. I once changed a master cylinder for the same problem.
Did not solve, ended up being the caliper pins were seized.