Indicate that loading is in progress and hide charts for previous data period
There are currently two problems:
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If no data cached for a specific device token it takes some time to perform database queries (usually a few seconds) while loading the charts. This is not indicated by any visual object (e.g. a rotating round) and users don't know what does it do (Is it working? Or there is some problem?).
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The loaded charts are updated progressively (one-by-one). It means that some of them may be already update for the new time period whereas the other ones need not (and they show the previous time period). I suggest to hide all the charts before it starts loading the new ones.