android-security | app showcase of some techniques to improve Android app | Security library

I tryed to send a POST request to a remote secure server ( https call). First i used the OkHTTP lib to make the call, as this lib worked to make http calls in a previous app, but with https it does not work anymore, see my previous post : Cannot make HTTPS calls with OKHTTP lib

I decided to try the HttpURLConnection to make the call as explained here : https://developer.android.com/reference/java/net/HttpURLConnection.html The code I am using only works on certain devices.

It does work with a Wiko on android 6.0 equiped with SIM card and wifi and does not work on a Samsung on Android 4.2.2 only linked to internet via Wifi.

Here is a logcat of the problem I encounter :

I'm getting this error when I try to fetch the previously chosen private key when I recreate the activity after rotating the screen.

I've seen this question here, which suggests that choosePrivateKeyAlias() needs to be called "at least once after the application is installed". In this case it has been called numerous times, including when the app is started up before the screen rotation happens - so why is it considered to be a new app? Is the uid changing somehow?

Here's the call:

PrivateKey privateKey = KeyChain.getPrivateKey(getBaseContext(), alias);

I've just noticed that the other question was using getCertificateChain rather than getPrivateKey - is that the difference?