Can you please open cyfxtx.c file and check if the address 0x40078000 is specified as 2-stage bootloader address?
Yes, the cyfxtx.c file contains:
#define CY_U3P_SYS_MEM_TOP (0x40078000)
and the linker script cyfx3.ld for FX3BootAppGcc contains 0x40078000 as well (as start of the code)
SYS_MEM : ORIGIN = 0x40078000 LENGTH = 0x7000