Hi @Erik_van_den_Bergh ---- Thank you for the follow up and my apologies for the slow response.
Moving forward, it seems that you have identified the culprit here (i.e the additional Netgear router) 
In regard to Android versus IOS, and which of the two are more “sensitive”. We do not have reason to believe that one is more stable than the other, the strength of a device really comes down to the network in which it is communicating with.
Furthermore, while I am not certain how you have configured the additional Netgear router to extend your network, the best advice I can give you is that we recommend making use of a mesh network setup. Companies like Erro or Orbi, seem to be very reliable. Our CTO Brian, goes into further detail here in regard to the advantages offered by a good quality AC router or “mesh setup”.
-Eric