Its a file problem with not displaying the navigation bar. Alt + M is not working. If I mouse move over a known variable or anything else, that VA knows, I get a tooltip window with variable type for example, as expected.
If you close and reload the file, does the problem appear again? So is it always broken in these files? Or does it sometimes work in these files?
Is there any pattern to the files that have the problem? Are they under the folder your SLN file lives in? Are they part of your solution? Are they in stable external libraries?
What file extension or extensions show this problem? Do other files with the same file extensions work correctly? Or is it possible all files with this file extension have the problem?