I can confirm that an FPGA Board with the MAC address "0004a36dd5f2" was not produced by ZTEX.

The FPGA delivers wrong results from start-up. It's no overheating issue (but may be a defect caused by overheating). Probably the only thing you can "repair" by yourself are shortcuts, e.g. caused by electrical conductive thermal grease or metal (solder) remnants.