This issue is happening quite often with T212 but not in any of my other platforms.
On my ISA, I trade quite liquid stocks (average volume >300k), sometimes at market open my stop gets hit whilst the price was never close. I understand the spread is wider pre-market, so it’s like at market open the stop is hit by pre-market spread and not by the new market open spread.
Never use stop loss orders to avoid this problem and to avoid spikes in the market or market manipulation triggering orders only for the price to then revert back to normal.
I don’t know but somewhere in my distant memory I seem to remember some platforms disabling stop losses triggering at market open but I might just be imagining this.
I don’t know if it is part of the answer but on some chart packages/systems you sometimes see very large spikes occasionally. I assume that it can happen when one side of the order book gets cleared and could happen at market open if there aren’t many orders on one side of the book and a market maker has an order to fill. My suspicion (nothing to back this up except a cynical mind) is that its one way to legitimately manipulate the market but causing a momentary price spike that triggers stop loss or limit orders (depending which side the spike occurs).
I wouldn’t be surprised if there is a brief moment at market open where the order book hasn’t been filled with the new orders for that day and thus may be weaker then other times during the day.