Sometimes your wi-fi may be spotty or your bandwidth may become constrained. This may be a result of multiple photos and videos being uploaded or your simply because your internet service may have a slower day.
To easily clear the events line up in your queue, simply turn on your device’s airplane mode. Wait for 30 seconds and turn airplane mode back off. This will force the device to resynchronize with your wi-fi and it should start sending through the queued events.