Receiving Notification Push

Good morning guys.

I have a problem with notifications push on android (any version).
In practice, after a while some of my clients' terminals don't receive any more notifications until they clear the app cache (I found this solution after several attempts and tests. It works 100%.).
Why after a while is't necessary to empty the cache to receive notifications? Is't a common practice?
Is't normal empty the cache every so often to keep the reception system working?

thanks a lot to everyone.

 

UPDATE:
After several tests I discovered that on some Android versions (especially starting from version 7.1.1 onwards) if the app doesn't have the automatic start active, the notifications aren't shown.
I tried to start a service in the background but as with notifications, the service is also deleted when the user removes the app from the ram manager.
I can't deal with it. Has anyone dealt with this problem before me? Please help me. Thanks.