If you click on positions < Missed, there will be an explanation for every missed trade. Such as not enough money in balance. Or market not available etc.
The system will send out the request and await a response from the broker server, it wait's for a response for 15 minutes. As long as the trade remains within the price parameters set by the signal, the trade will be executed within those 15 minutes. After 15 minutes the trade will not be copied. This is why your trade execution could be late.