I had the same problem. Everything working fine using 3G but not over wifi. Not a specific one, just using wifi in general made the client impossible to communicate. Didn’t find any hint to the problem. No matter whether I’m accessing via IPv6 or not. In fact the webservers log do not even show any attempt to access the site at all after connection has been tested. The phone does not try to connect and then states it took too long. I don’t remember it happening before I changed my password but could be the case that the app did not work for a while using wifi.
However, I can use the Android-cilent over Wifi again after I activated 2-factor-authentification and generated an app-passwort for the Android-client. I think this is even better than storing the same password everywhere.