It may be your AUC3 converter, between the controller and the miner. Do you have a spare one by chance? If you do try swapping it out.

I know in the past a few have gone out that weren't flashed for operation.

What do the lights look like on the miner and on the AUC3 converter?

I tried using my old controller with my Avalon 821's but had the same problem as you! I discovered that you need to upgrade the controller firmware to the newest version that supports the 8's.

Hope this works for you!