Are you searching over all time?
Note, I've had some issues surrounding empty buckets gone missing at the beginning or end of a timechart in the past, not sure if they still exist. If you're not searching over all time and not setting fixedrange=f but still don't get buckets with count=0 at the beginning or end that would fall within the timerange but don't have any data in them you should file a case that timechart is a bit broken here.
Have you considered a search for all your sources and a count by source to get one chart?
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