Master Cylinder replaced, brakes won't bleed

[Rswearing]

I am at my wits' end here.

06 X5 4.4.

Put on a new master cylinder. Bench bled - no bubbles, just fluid cycling through the lines.

Installed with the hoses still on the bleeder and submerged in the reservoir. Pumped brake to be sure still primed. Nothing but fluid cycling from both ports back to the reservoir.

Disconnected bleeder nipples and attached brake lines. Pumped brake - no pressure building. Opened bleeder valve on the rear wheel - will not bleed. Opened valve on the front wheel - will not bleed.

Fluid in reservoir not dropping.

Help please. I cannot imagine what I'm missing here.