Once I leave the brewing room to go elsewhere, getting hops for exemple, the connection between the phone and the GF (G30 here) is lost. Once the tie is broke, it is impossible to re-connect.
G30 - Android Phone, latest version of the app

Hi Pierre,
Will you be able to tell us which Android device you are using and what version of Android it is on?
And can you please check if the “Performance Optimisation” option is turned on in the Preferences page in the last tab of the app?
Hi,
I have a Xiaomi Redmin Note 9 Pro running on MIUI 12 (version 12.5.1) based on Android 11 RKQ1.200826.002.
Performance Optimisation was turned off, I didn’t knew there was such an option. I turned it on.

With the Performance Optimisation turned on, we believe you will no longer face reconnection issues :)
On some android devices, the OS kills the app agressively when it is not open, the Performance optimisation prevents that from happening only during an active brew. Please let us know if you face issues with re-connection during your next brew session.

Another thing that improves reconnection reliability is to turn off Battery optimisation for this app atleast during a brew session.
To do this,
Open your phone settings -> search for “battery optimisation”
-> Tap on “Battery Optimisation”
-> Scroll down till you find the Grainfather app and tap on it
-> Change the selection to “Don’t optimise”
With this we can guarentee that you won’t have reconnection issues throughout your brew.
We don’t run any background processess when there is no active brew session, so it is safe to keep this option as “Don’t optimise”