In which cases does a signal get rejected (skipped for execution)?

A signal has been rejected on the order management level, if signals quantity at the "Signals" tab equals to 0 and there is no orders on this signal.
For example, if a signal for selling is received, but there are no such stocks for the account.
Another example: if conditions are triggered (e.g. crossover of indicators), but the signal has not been received (i.e. there are no arrows and signs for that bar).
The reason is in the algorithm of position size calculating.
Another example: signal is rejected, if it is received for buying stocks worth 10% of the account, but there is only 5% of the account which is available, taking into account the leverage.
To buy for remaining funds, set the option "Buy for remaining funds" at the "Strategies" tab in the settings.