String deconstructor throws runtime exception

Only recently has this problem been occurring. I've tried cleaning and rebuilding the solution with no luck. I've traced the exception to these function calls:

std::string::clear() {
     _Eos(0);
}

which invokes

void _Eos(const size_type _Newsize) {   
    // set new length and null terminator
    auto& _My_data = this->_Get_data();
    _Traits::assign(_My_data._Myptr()[_My_data._Mysize = _Newsize], _Elem());
}

And raises the exception here:

static _CHAR_TRAITS_CONSTEXPR void assign(char& _Left, const char& _Right) _NOEXCEPT
    {   // assign an element
    _Left = _Right;
    }

Acess violation _Right is 0 '\0'

I'm using Microsoft VS Community 2017