MCU Crash / restart- PIC24EP512GU810 RESTART_TRAP_CONFLICT ?

[Ttelmah]

Jeremiah may well be right. Your chip is one of the family that does have
oscillator issues. The XT oscillator has issues (which is why you are selecting
HS), but this can give problems when running from 4MHz, with unreliable
startup. The behaviour can lead to odd instruction execution during the
boot up. Can I suggest you just try the experiment of using the internal
oscillator instead?. It will give poor timing accuracy compared to the crystal,
but if the issue disappears you know where the problem is. If you have a
faster crystal available (8MHz+), this might well fix the problem.

[temtronic]

also... might try a oscillator module ? Heck it even frees up an I/O pin !!