I don’t understand how hard it is to differentiate between wrongly executed orders and not executed orders that would be great for the users if they would. You have every right to ask corrections if the execution is not correct but why would broker (or the stock exchange) would pay you for an execution that did not happen at the first place? Broker is only responsible for providing the best execution price if the execution happens. It is not guaranteed that an order would instantly happen or that the price will not fluctuate at the instant of execution.
One can get frustrated when e.g. orders not going for half an hour after the stock exchange opening, and may prefer another broker if they provide better executions, but asking for reimbursements for not executed would-have-been-great orders seems odd to me.