I changed my site times as per date/time zone fixes a few days ago. Now my member growth chart does not display. I checked a few forum posts for fixes and saw that if people put tomorrow as the end date then the display returns. And so it did for me! This leads me to think that the growth charts are doing a date reference for the end date that needs to be today but as my site time is now +10 then something is not quite in sync. Most likely the growth charts are accessing server time and as I have set +10 for all website times then there will only be a "today" for the time period that my server time in the USA and my website on Australia time are the same. Haven't done the calculation. This would account for people reporting that their growth charts "magically" reappeared and then disappeared again.
It looks like time/date issues will be taken care of in D8 but perhaps a code improvement to the growth charts could be included in any updates to D7.1
Cheers all
Tassieswingers