What is gap risk? That’s the adverse effect on your position that a gap in price form last to next price may have. I haven’t seen any for a while in the markets I follow but they do happen. So bar 1 closes at 140.00 (Eur/Jpy) and bar 2 opens at 140.75, significant gap, and it may even be much more than your initial stop loss creating a greater than expected loss. Technically most of the time the gap will be closed, even if the market is to continue in the trend of the gap. However that doesn’t stop you from being taken out at an usually expensive level!! They tend to happen when the markets are close, over the weekend news may come out that affects the markets but they are not open so the price can’t move accordingly, then Sunday evening the markets open and it’s far away from its close on Friday. What’s the solution? Easy always be flat by Friday close.
Gaps opening in price action can knock you out for sure. Like you are saying they are worse when the market is closed or between once timezone and another. Brokers can also handle the events how they like which is why i close out on weekends.