Visual Studio 2015 Debugging: Can't expand local variables?

It might be a bug. Please file a Connect bug with a repro if you have one.

In the meantime, you might be able to workaround the problem by setting the debugger options to use the legacy debug engine: Tools -> Options -> Debugging -> General: check both "Use the legacy C# and VB expression evaluators" and "Use Managed Compatibility Mode".

That workaround has worked for me every time. But please, do still file the bugs!

I had a similar issue where when I hovered over my local variable, some would let me dive deeper and some would not show anything. After some digging I found an article on msdn here, that suggested resetting the settings in VS. Once I did that, I got a notice that I was running in Release mode and that some debugging features may not be available. Once I changed to Debug mode, everything worked like normal.

Hopefully this will work for you as well.

As described here, you need to enable the check “Suppress JIT optimizations on module load (Managed only)” in Debug --> Options --> Debugging --> General.

You need also to remove the "Optimize code" flag in the properties of your projects.