Some ideas:
Search for something that you know is in the data over all time. Perhaps there is a timestamp problem, and the data is really in there, but not at the time you expect.
Search index=* for that data. It shouldn't have happened, but what the heck.
Is the data recent? If it is older, or has widely varying timestamps, you may need to set some rules in props.conf. Put them in props.conf on the indexer if you are using the Universal Forwarder. Look at the settings for MAX_DAYS_AGO , MAX_DAYS_HENCE , MAX_DIFF_SECS_AGO and MAX_DIFF_SECS_HENCE in props.conf
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