Sorry so hear that you're still having problems. The built-in BEC shouldn't be required for basic use case. Unless you're trying to power some other on-board electronics/avionics with the BEC.
All you should need is the "power in" to all 4 esc's from a PDB and then signal and ground from esc's to flight core J7, via the breakout board.
Modalai's breakout board was designed for PWM signals only and works well in that regard. Also check to make sure that
is set to "disable"
Here's some notes from our board designer to clarify.
The primary design intent was to be used with a distribution board for power
It is actually unsafe for these types of pin headers to have exposed voltages on them
We wanted to prevent some customers from accidentally installing two BEC generators on these blocks which occur all the time in other hobbyist forums/kits and customers end up damaging their BEC modules.
We apologize we did not make it clearer this is just a breakout board and not a BEC distribution block.