Why does a fill get slow or rejected right when price runs your way?

[Shadow Trader]

Picture a clean break of a minor level on EURUSD. A buy market order goes out at 1.08420, price ticks up to 1.08435 in the time it takes the request to reach the server, and the platform answers with a reject, or a fill that takes a beat longer than usual. The same order sent a second later, with price drifting the other way, comes back instantly at the requested level.

That asymmetry is what people usually describe when they talk about last look. Some liquidity providers keep a short window in which they can accept or decline a trade after it has been sent. A decline is far more likely when the market has moved against the provider since the quote, which means in favor of the client. Whether any of this applies depends on the broker's liquidity setup, and the platform will never label it for you.

What it tends to look like from the terminal side:

- A delay of a few hundred milliseconds that only shows up on winning-direction moves
- Rejections that cluster around news candles and fast breakouts
- Identical orders in quiet conditions filling with no hesitation

The tell is the pattern, not any single event. One slow fill proves nothing, because network jitter does the same thing. A few dozen fills split into "price moved for you" and "price moved against you", with timestamps from the platform journal, is a different story.

Also worth noticing: a wide open deviation setting gives the provider room to fill at a worse price instead of rejecting, so the rejection rate can drop while the average entry quietly gets worse. Which of the two shows up depends on how the order was configured.

Has anyone logged journal timestamps by direction of move to see whether the delay is really lopsided on their broker?