Invites and Friends

I own a Samsung S7 Edge and when I open Minecraft Pocket Edition, I don't see my friends online but I know for a fact they are playing online as I have spoken to them by other means of communication, which they tell me that they are currently online and playing. As for invites, whenever I don't see my friend online playing, they will usually send me an invite to their server/world to play. However, I haven't gotten a single invite. Whenever I invite them, they never receive it. Also, when they do see me online and playing, they can't seem to join unless:

1. I restart the game.
2. Restart my phone
3. Uninstall and reinstall the game
4. Wait until the next day or a week before trying again.

Please fix this. It's been like this for months since I installed the game.