Can't close open positions for 15 seconds

Does anyone know why the buttons for closing open positions are disabled at times? 

This is not the first occurrence, and there are instances where I cannot close open positions for 15 seconds or more. 

When I click on the Cross button, it doesn't allow me to close the open positions.

What could be the reason for cTrader (or the broker) canceling my orders to close open positions?

The cTrader had a stable internet connection throughout this period.