Resolution

It did in fact crash twice, and was therefore reinstalled and have had no issues since. It is assumed that the OS was corrupted after the first crash.

The old server was running some RAM tests multiple times, even on each stick, and was found that one stick had one bit being always on. As RAM usage is pretty random, this may have been the reason for it crashing. Two sticks were removed, as it can only run in pair. It wont be online, but at least it is known to be working now. The stick could still be used if told the kernel that memory bank not to be used, but it was a risky thing to do and will the thrown away instead.