Two identical trackers, different results

As we intend to migrate Piwik form an externally hosted server to one of our own, I set up the websites with two trackers, to have a fallback, if something goes wrong during or after migration.
Both instances of Piwik work, unfortunately, they have different results (e.g. 11936 visitors/day and 9761visitors/day)

Both Piwik are version 1.11.1, both use the same script, both have thesame setting (I imported a db-dump from one server to the other one).

Does anyone have a hint for me, where to look for the cause of those differences?


Maybe one has DoNotTrack support disabled and the other one not?