P8_43 prevents board from booting?

I have P8_43 (Pin 42) set up for 0x00000005 in a device tree overlay however my board fails to boot when the pin is connected to my circuit. I have other pins with the same setup and in the same circuit configurtion that work fine, and I have swapped around the board pin/breadboard pins so I know for sure it is the pin the p8_43 header connection causing the problem. This is also the first time I have connected anything to this particular pin. Is the pin dead, or could it’s default mode before loading my .dtbo be causing the problem?

The power and ethernet LEDs light up but none of the USER LEDs do, and I cannot ssh into it. When I disconnect the p8_43 header connection everything boots fine. I have also checked to make sure the pin is indeed set correctly in my overlay and there are no errors in loading the overlay.

doh, just read the SRM.

You mean the boot pin that sets the boot sequence for the processor? You should not hang anything on there until after the board boots. This is covered in the System Reference Manual.