eDiscovery index error

I am receiving an error, MaxItemsExceeded, when I index data I added to an advanced ediscovery case.  I added 10 custodians and their data both exchange and one drive.  Instead of indexing all the data I indexed one custodian at time and am now receiving the error on one custodian.  The others completed.  How do I get around this error?  I am assuming I am hitting a limit in advanced ediscovery.  Can I separate email from onedrive data?