Alt Enter not working in VS2017 15.5.2

I'm trying to get Alt+Enter to work in VS2017 15.5.2 Enterprise on my machine.

I tried to reapply the Visual Studio keyboard scheme in R# options and reset Visual Studio's keyboard shortcuts multiple times.

I assigned the Alt+Enter shortcut in the keyboard settings to the ReSharper_AltEnter shortcut entry.

I noticed four things about the AltEnter behaviour:

1.) If I start Visual Studio by opening a solution directly, I can use AltEnter as usual until Visual Studio is fully loaded. So Resharper seems to correctly detect and process the Alt+Enter shortcut while it is loading.

2.) After Visual Studio is fully loaded, everytime I use Alt+Enter I just get the "Enter Action Name: " menu popup, the same  you get if you use "Ctrl+Shift+A" (GoToAction). So despite having set GoToAction and AltEnter to different shortcuts (Ctrl+Shift+A and Alt+Enter respectively) both shortcuts open the same popup menu.

3.) I don't know if this helps but I also noticed that the quick actions shortcut of VS (Ctrl+.) doesn't work if I have ReSharper loaded. I tried to assign Ctrl+. to ReSharper_AltEnter, too, but without any (visible) effect.

4.) I also noticed that AltEnter just doesn't seem to work when editing .cs files (more general if I'm in the code editor) but if I work in the XAML designer view and edit xaml code, the regular AltEnter context menu works just fine.

Is there anything else I can try or is this a known bug? I really would like to use the regular AltEnter context menu again.