Error highlighting in project view works only if file is open (scala)

I enabled the "Highlight nodes with errors" option of the scala plugin in order to highlight files that contain errors with squiggly red underline inside the project view.

It works with one minor and one major issues.

The minor issue is that it takes a bit of time before a file is highlighted in the project view, even though the error detection is immediate in the editor view.

The deal breaker issue is that the highlighting in project view seems to work only if the file is currently open in the editor. Since I have a very large number of files in the project that I can not possibly have opened at all times, it makes the feature not very useful. Ideally when a change I make in a file that is being edited introduces errors elsewhere in the project, the errors would be highlighted in the project view even if the other files where the errors occur are not opened.

I have read that building the project could solve the issue, but for reasons I won't go into here, I do not use Intellij to build the project. The build is done outside of Intellij in the runtime environment of a software for which I'm writing some extensions.

If this is not the place to ask this question, I would be great to know the best place to post this issue.

Thanks in advance.