Can you measure the Drain to source voltage across each of the MOSFET's in your circuit during startup?
The high side FETs are about 23.3V
The low sides (Q1: 2.8V, Q2: 0.1V, Q3: 1.4V)
Can you measure the voltage across ISEN during startup?
The voltage across R5 is 0.049V, which means i'm drawing less than 1A of current through it.