You'll want to check the bell settings for that channel to see if you've opted-in to receive all notifications. It's possible you may be on the default setting to receive notifications occasionally. Here's more info on this: https://goo.gl/giVA8o . Let us know if this helps.
Thanks for the info! Could you try signing out of your account and sign back in, Also, restart your device. Let us know if that clears up things.