Hi @gabi83f
I’m afraid this issue is more related to Google Maps and Bootstrap than ACF. Searching on the internet, I could find several threads that have the same issue like these two: http://stackoverflow.com/questions/17187903/google-maps-marker-not-center-after-resize-on-bootstrap-tab, https://groups.google.com/forum/#!topic/twitter-bootstrap-stackoverflow/T3z5SrwNBCg.
In this case, could you please get in touch with Bootstrap or Google Maps community?
Thanks 🙂