Unfortunately that's known behaviour for nimsuggest (in fact it used to be worse).
If you haven't already setting up a project file, do that. If that doesn't bring any improvement, I fear it's time to say adieu nimsuggest, it's not the most reliable tool in the world (the addon has an option to do that). You will still be eable to receive error messages in editor, because those (by default) are served by `nim check`.
