Hi, i think i have the awnser for you : To Fix FCPX Crash When Using Intel and GPU AMD or NVIDIA Dual.
1) Install with the Last Multibeast (For 10.14.4, please use Multibeast 11.1.0)
2) Select in Graphics the Patch AKA WhatEvergreen and Only That !!!!
3) Open your Clover Config file with Clover Configurator
4) In Graphics section, you have to choose the IntelChipsetVGA for your Motherboard(CPU)
5) In the Menu Choose from ig-plateform-id (For me in example it's 19120001, i have a Skylake CPU HD530)
6) Now you have to Patch the GFX from Acpi section
7) In List of patch Select GFX0 to IGPU
8) Save and Reboot that All
I Run HD530 and AMD Saphire 580 in Dual, and Get FCPX and quicksync PERFECT and FAST.