oOGenosOo

Never try on NetCore but fews days ago i'd the same problem on an Android Project (Mono framework) and i solve doing a right click to my droid platform project...

Seems to be a Contect Problem, your context not exist when you call it, look here for more informations: https://stackoverflow.com/questions/38298887/logout-dialog-error-token-android-os-binderproxy4276c0e8-is-not-valid-is-your

Maybe is not a problem of android 4 but a problem of device speed, an android 4 device is slower (faster if is an emulator) that a newer one, and...