Google Analytics+ suddenly shows 0 traffic

I have a problem with the Google Analytics+ plugin on all of our blogs. Sometimes it shows 0 traffic on the blogs on the current day or day before. If the user refreshes the page several times, then it sometimes show the correct statistics.

It is happening on all of our blogs in the network, no matter of theme and active plugins. I have tried deactivating all plugins and switching theme, but none of them have worked so far, so I don't know what is causing it to suddenly show 0 traffic, and one moment later, shows the correct statistics.