Sounds to me that either the Fast Blanking voltage is either too high or too low.
I suspect you have one of "Those" display panels that is some what very temperamental on the input voltage that selects RGB.
Pin 16 is of the SCART is the decider here, you need to know the following
1. What voltage is being supplied (I suspect 5vcc but CHECK with AmigaKit)
2. What resistor is being applies (I suspect something like 330Ohms - check)
3. What load resistor is in the LCD panel (and this is the bit that will require a bit of effort)
From what I had read here, I suspect that this LCD TV Panel has a higher than 75ohm pull down (on pin 16) - if this is so, then its possible the input voltage is too low < 1volt pp.
While unlikely it is possible that there is NO pull down on the input of pin 16 which would mean the voltage could be to high > 3v pp.
I seriously suspect the former and you will have to investigate more.
Firstly I only encourage you to contact AmigaKit where you purchased the cable to seek their advice, for me to attempt a work-around, I would drop the input resistor 100 Ohms and see what happened.