The customer in this case had moved many archives over to Exchange around the time they upgraded from EV 9.x up to EV 10.x. Because of this, there were no new items going into the Domino 64bit indexes leaving them with high start number going to Not Set, and Not yet Created. The condition then occurs if you run the rebuild index task on this archive after the 32bit indexes have been expired and the 32bit index has been deleted. The rebuild index job assumes that if there is a newly created index with no items that the start number must be 1 and so when the start number is higher it fails. The issue is minor in that there are really no items left to be indexed.
 

Workaround

Determine that there are no items left in the archive to be indexed by running a report on the vault store. Right click on Vault Store and click report. Then select View usage report by Billing Account. Find the archive in the report. If the archive has zero items you could choose to delete the archive.

This issue has been addressed in the following release:

Enterprise Vault 11.0.1 Cumulative Hotfix 1 Release
https://www.veritas.com/docs/000024613