Connection problems or burned chip?
You applied solder paste by hand and soldered with hot air.
The chip has a large thermal pad underneath that is connected to ground.
You have pins reading 0 V when there should be some higher voltage present.

I think you've got short circuits between the thermal pad and some of the pins.  The shorts will be under the chip where you can't see them.
Measure the resistance between your anomalous zero volt pins and ground.  I think you will find things are shorted.

Remove the chip with your hot air station.
Install a new chip. I think you'll want to replace the old one because there's no telling what damage may have been caused by the short circuits.
Use less solder paste on the thermal pad than you did the first time.

Next time, measure the resistance between all pins and ground before you apply power to the circuit.

If you have time and resources enough (moola to have a new PCB made,) then you can make it easier to install the chip.
Place a large plated through hole under the chip.  You want it as big as possible, but still smaller than the thermal pad.
Install the chip as usual from the top side any way you like (I'd solder it by hand with a small tipped iron, but I'm weird that way.)  Do not put solder paste on the PCB pad for the thermal pad.
Once all the pins are soldered and there are no short circuits, flip the board over.
Put a drop of liquid flux in the plated through hole for the thermal pad.
Use a large tip on your soldering iron, and solder the thermal pad to the plated through hole.  Keep feeding in solder as long as it'll go in.
The solder should wick its way in under the chip and make a good connection between the thermal pad and the PCB.