Anyone have an idea why this downward spike occurs and how to protect against it?
If Only.
I was watching TradeBrigade premarket comments live, the other day, and he had one. He said wow, one of the other viewers chacked on TradingView and yep, it was there too.
So they have all the attributes, damn them, of a real trade.
They turn a Stop-loss into a Cause-loss, as maybe you found? 
I stopped using Stop-Sell orders and Stop-Limit sell orders here, as something on the chart triggers them in error. Too Risky.
If you really want to use one, I found if you put a price alert there first and THAT triggers in error, then a stop-sell will trigger too. Half a minute later it’ll settle down, if you’re lucky.