freezing can be attributed to a number of things although principally heat is one of the major causes. Can you post when the freezes happen? Is it when you do something particular like gaming or just random?
Check your temps using an app such as this: http://www.hwinfo.com/
Check your temps at various points. Alt-Tab out of games to quickly check your temps as often your temps can be higher when gaming than when using a stress test so it's important to check.
System lock ups can be caused by many things but I agree, it is probably not the board - unless it is covered in a layer of heat-trapping dust. Other common causes are a failing power supply, corrupt system files, and malware.
I have seen intermittent behavior like you describe caused by wonky SATA controllers but most likely by power supply age and/or condition. Overclocking can cause things to go odd, as well.
I would pull out every extra thing beyond boot drive, mouse, keyboard and monitor, including Bluetooth, wifi and LAN to eliminate everything but the basics. Should you have a PSU tester or can borrow one, please use it. After pulling things apart, try each extra piece one at a time to try to determine where the problem reappears. Good luck.
My point about the RAM QVL is there is are just too many RAM makers producing too many RAM models for motherboard makers to test them all. It would be way too expensive and those costs, naturally, would have to be passed on to us consumers.
Because there are so many, board makers (not just Gigabyte) should not be expected to figure all that out. So they test a representative sampling of what's out there.
We don't have to buy listed RAM, but we do have to buy RAM with the same specs as listed RAM to ensure compatibility. This is why in your motherboard manual, it says to refer to the motherboard's website for a list of supported RAM (page 8).
Note for CPUs, it is different. Because motherboards support either Intel or AMD CPUs, and because the chipsets on the motherboards support small families of CPUs within either Intel or AMD, there are only a relatively few number of CPUs from one maker only the board supports, so the motherboard makers can test them all. So you do need to buy a listed CPU.