When I launch Avast Mobile Security it runs for a few moments and then disappear. I tried to run it from Avast Cleanup but it starts to run trash scan and then also turns off. Also I’ve noticed that AMS trying to send notification in notification bar but its only blinks for a short moment stating Protecting this device.
I tried to reinstall AMS but it still doesn’t want to run.
What kind of device do you have? From your description it seems that either the app is silently crashing, or that the system kills it because of low resources.
Ondra