Line Lock problems!!!!!

This is so simple
The LLs job is to prevent the brake fluid from returning to the M/C. Yours is not doing that.

But you have another issue as well.
One caliper is locking onto the rotor as per the design while the other is not. Both calipers receive their fluid from the same T-block right? Well in order for one to slip,there has to be something wrong in the circuit or a mechanical problem in the sliders or pistons, or bent pads.

Now, the piston for the safety sw in the C-valve is sealed from both sides. It can sense a difference in front to rear pressure, and then turn the dash light on. But it is sealed from both sides, or is supposed to be. But it doesn't really matter because your LL is installed between the the C-valve and the new T-block. So even if that piston was leaking it would not affect the T-block. Neither can the rear system affect it, cuz it too is on the wrong side of the LL. So the LL is just not powerful enough to keep the fluid from returning.
Since this is your second or third Biondo, I suggest a different brand.
But I would still look into the RF failure to lock onto the rotor.

BTW
I have an old Hurst set-up from the 70s. If I didn't set it right initially, I can add hydraulic pressure without resetting the solenoid.The fluid will pass freely forward to the calipers from the M/C. Sometimes I use it as a hill-holder with my stick car.I use a separate toggle sw for this, cuz like who wants to hold the momentary for two minutes, right?lol.

Because you have one unused port on the C-valve, if you wanted to, you could plumb a gauge in there And see exactly what's going on.