Minecraft – iPad mini 2 settings for local MCPE (0.12.1) server

My son and I have a problem creating and joining a local MCPE (0.12.1) server with his new iPad mini 2 (iOS 8.4.1 (12H321)).
I know this might be a tough one to "break" – Cause there's A LOT of settings to poke around with on the iPad.

I have an old iPad 1 (OS 5.1.1 (9B206)) and a Samsung Galaxy Tab (don't know which one) both tablets have MCPE 0.12.1 installed.
These two tabs have no problem creating/hosting/joining a local server – But the Mini can't see or join a server created with the above tablets. But! sometimes we're able to get it to show and join/host a server right after it has been rebooted – But after a minute or two it disconnects.

Wifi signal is very good – "Local Server Multiplayer" is enabled on all tablets – We're also using the correct IP's/ports.

Therefore I think it has to do with some of the settings on the Mini.

So the question is: Which settings is NEEDED AS A MINIMUM to be enabled/disabled on the Mini to be able to host/join a local MCPE (0.12.1) server??