1995 Eagle Vision My car doesn't brake properly

I recently replaced the rear brake lines because there was leaking. During the bleeding l realized that there is almost no pressure at the end of the left rear pipe (before the hose). Before the leaking happened, the brake system was working really poorly, no wheels locked out even if you pressed as hard as possible on the pedal. Now only the front right wheel locks out when you press really hard the pedal.

What may be causing this problem?

Does an improperly functioning of the proportioning valve cause a loosening of pressure in the system?

Thanks for your help.