I think I've figured it out: tried it in another location and as soon as it says "The homepoint has been updated" it starts to ascend higher than the 5 metres limit.
Yes, there is a cutoff based on the wifi strength of the mobil device. If you go into your settings it should be locked both ways distance and altitude. Don’t remember exactly, since I use an RC. But DJI states the max altitude around that high.