ok, so the changing length of the event notifications is probably just down to repeated triggers extending the length of each notification. (e.g. if the event is triggered multiple times very close together they will all be clumped together into one notification) When you are actually recording by event you can set a pre/post record time to try and limit the duration of each event recording, but the same cannot be done for event notifications.
The only way to reduce the length of these notifications is to play around with the event settings to reduce how frequently the events are being triggered.
In regards to the 'No Video' error, Do you see this on all the cameras you have or just one specific model? If it is just one model which model is it?
How do you have the recording schedule for the problem camera set? Continuous, motion, event, or something else? (can you send us a screenshot of the recording schedule for the problem camera)