Make sure none of the mosfets are touching each other. Other than that I’m not sure what can cause that. It shouldn’t do anything until you tell the heaters to turn on. If the indicator LED’s are on without turning on the heaters you have a bad mosfet, and will need to replace it. They are only $1-$2.
I have fried a few of them. It usually happens when voltage testing. Hit that probe on the wrong thing and boom, bad mosfet.
The beta firmware is setup for a heated bed. https://www.vicious1.com/forum/topic/need-some-beta-testers-for-some-new-firmware-stock-machines-only-please/