This is an old problem ... I am guessing that what has happened is..
That your stop is in fact converted into a limit order - whereby your stop and limit are at the same (or very close) price.
If your stop-loss order was converted to a limit order, and if the exchange was unable to sell at that price as the price had already dropped through that level, then your order would not get executed...
I have removed the rest of your message as it is based on a wrong premise. No, it was not a stop-loss order. I learned not to ever use stop-orders on Kraken as they simply don't work as intended (exactly as you are describing). I underatand stop loss orders are NOT on the order book until they get triggered and inserted (whenever that happens) in the order book. This has NOTHING to do with that.
It was LIMIT ORDERS, opened several days in advance, already on the order book that HAVE NOT BEEN EXECUTED YET THE PRICE HAS KEPT RISING ABOVE THEM.
When I say the trading engine/order book in Kraken is broken I really mean it. There is absolutely no technical explanation to this. The only doubt I have is WHO profited from it.