I've seen this issue before where there are too many invents within a subsecond timespan for Splunk to process. Newer versions of Splunk know this and actually increment the timestamp at indexing to prevent this from happening.
Yes, you could increase the max_rawsize_perchunk (Splunk recommended that we set this to a really high value , or unlimited, but it caused browser issues for us).
You should also look into that data to see why there are so many events being returned within the same sub second. It could be a bad timestamping issue or lack of timestamp in your event causing Splunk to have to use the current time as the timestamp.
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