Resharper cannot find protected member, although the compiler can Follow

I get errors from Resharper if a templated sub-class tries to access a protected field in the base class.

In this example

template <typename T>
class Base
{
protected:
   T _x = 0.0;
};

template <typename T>
class Sub : public Base<T>
{
T fn()
{
   return _x; // This is where squiggles appear
}
};

the final _x is squiggly and it says "cannot resolve symbol _x".

If I turn Resharper code analysis off, it is goes away and it compiles either way.

Is there a reason for this, or an option that will disable the squiggles?

I am using VS 2017 15.8.4 with Intel C++19