Still getting those x's but different spots and different boards with each reset
It might be a hardware if everything in software not working like ccgllc said it may be dying. For now better to adjust and lower the frequency of your miners, like what you said before it is working with adjusting frequency and fan. So, for now, this is the only best solution.
If you want to do hardware it would be riskier than software.
Anyway I wanted to share this thread it might be helpful for repairing s7 miner
https://bitcointalk.org/index.php?topic=1420909.0