BMW head unit losing memory after some time

I have bought an aftermarket head unit and a harness adaptor for the BMW.

I’m not great with cars but thought I’d give this a go myself. The harness has a flying red wire which required connection to power. Originally I tried connecting it leaving the red wire unconnected and as you’d probably guess the head unit didn’t turn on.

After some reading, every one suggested connecting the red wire into the fuse board (12V), which I have done. I have wired it into an ignition power slot otherwise the head unit remained permanently on. The head unit boots (after about 20 seconds of loading the Android interface) and I can change settings etc, and turn ignition off. If I then turn ignition on again it loads straight away and remembers my settings. However, if I leave it for a longer duration of time it resets the settings next time I turn ignition on, and I get the Android loading screen again.

I have tried changing the red/yellow wires and from what I can see the wires are correctly wired. I have tested with a multimeter to ensure I have permanent/ignition power as and when it should.

I’ve read the ground wire could be the issue, but assumed the harness I bought deals with this. Does any one have any ideas?