I run both piwik and google analytics on my site. I have noticed that the google analytics data is totally wrong. It does not seem to register any hits while piwik does. What could be wrong?
One possible explanation is that some of your users block Google Analytics. This is common, for instance, if you use NoScript in Firefox.
Have you used the google analytics debugger for chrome? https://chrome.google.com/webstore/detail/google-analytics-debugger/jnkmfdileelhofjcijamephohjechhna?hl=en
That shows in the developer tools console when things are firing.
Also is the site / GA account new, or are you taking over from a previous webmaster? If you are taking it over then have you checked that there isn't some crazy filter in place in GA?
One of the ways may be that your Google Analytics code is placed wrong (not sitewide block) or it conflicts with some other JS codes (e.g. old GA code).