UPDATE (10 Jul 2017)
Microsoft publicly released on this day the Android version of Skype for Business 18.104.22.168.
The two Exchange settings “Skype for Business Anmeldeinformationen verwenden” and “Server automatisch erkennen” are now by default enabled regardless of previous states. A user must explicitly override the latter (off) to get EWS to work if auto config is not desired.
Likewise a user interface quirk as last reported, if “Skype for Business Anmeldeinformationen verwenden” is activated, the UI disables it when you revisit the config page. The option “Server automatisch erkennen” now correctly remains off with the given URL if configured as such before. As long as you hit Cancel and do not logoff, all should continue to function.
Note that IMs received over the Android mobile client remain on the main page until deleted. To do this, press and hold to pick the delete menu option. Simply trying to swipe away does not (yet?) delete an IM from the list.