So those drivers are the same as we use, drv8825. You need to add cooling at anything above .7V heatsink and a fan. If those drivers were built corrctly you will be adding the heatsink to the bottom of the board and will need a fan on it. The way you have them mounted might be causing them to have thermal shutdown from being mounted hot side close to the board.
Reply To: machine gone rogue! (motors at least)