FAQs: GA Suggestions

This is a normal scenario when no GA code is used on a website.
Google Analytics code is not loaded via a traditional script snippet, nor it is injected via Google Tag Manager (and the tool knows it because no GTM code was detected either).

Case of no GA code detected.

Keep in mind that "GA Suggestions" is considering Google Analytics as the only analytics tracking tool, and Google Tag Manager as the only tag management solution. One might use another analytics script like Yandex.Metrika, and/or another tag management solution.

This particular case is reported as a warning, something that could or could not be an error and requires you to double check.
The tool is able to recognize the presence of the default Google Analytics setup scripts (several versions of it) and/or the setup script for GTM and does a great job in detecting their presence or absence throughout the whole site pages.
For performance reasons it does not execute the scripts in search of local javascript variables, so it cannot know if GTM is loading the GA script. In the case where no GA script is detected (normally an error, assuming GA is the your analytics tracker of choice) and GTM script is detected, it's up the the user to log in the GTM dashboard to check whether GA is configured there. The tool is still a great aid as it will pinpoint pages where the GTM script were not installed.

Case of GTM code detected, with not GA code. Not necessarily an error.

The point of strength of the tool is detecting with a single click issues with your GA scripts inspecting the whole crawled pages, testing a complete set of cases. Serious issues that too often would go unnoticed as one normally only inspects manually the home page only and for a single case. For an in-depth analysis, if needed, use page specific tools like the GA debugger from Google.

When Google Tag Manager is used, it is very common to use it also to inject GA code. The tool cannot know if GTM instantiates another GA script other than the one already instantiated with the GA code detected, causing a duplicate code issue. It is up to the user to log in GTM dashboard to check.

Case of both GA and GTM code detected. Not necessarily an error.

The reason why this is reported is because a very common mistake is migrating GA instantiation from the traditional setup code to Google Tag Manager, but forgetting to remove the old GA script from the template, thus causing visits to be recorded twice (and bounce rate dropping to almost zero).
Multiple scripts are serious mistakes because wrong analytics data can lead to take wrong decisions based on incorrect data.