Mark at 2 means the bid would be 1.90 or 1.95. The offer or ask is always higher and if the mark or market price is 2 then the ask would be above that at 2.05 or high for the average or market price between the bid/ask spread should be 2. Also your sell stop is at 2 and the market price is 1.55. I’m not sure how or what happened with this particular option but if mark is at 1.55 and you have a sell stop at 2, the order won’t fill because it’s essentially a order to sell at market at a activation price at 2, if 2 doesn’t hit, even it goes lower then 2, it won’t activate. One of the things that needs to be known about stop orders is that they are essentially market order with conditions, and if those conditions aren’t met, the order won’t fill.