Is the Indexing in Backup mode at all?
Another thing you can do is run a SQL Query against the vault store databases
USE EVVaultStore
SELECT COUNT(*) FROM JournalArchive WHERE IndexComitted = 0
This count will give you a list of all items awaiting still to be indexed.
The only thing that would really be stopping the indexing at this point would be read only
If its not in read only and there are a ton of items awaiting to be indexed, you need to get a dtrace of indexserver and whilst dtracing, immediately restart the indexing service
give it a few mins and stop the dtrace and just look to see if you can see any visible errors, and maybe create a case and submit that log or publish the log here if you're comfortable with it
https://www.linkedin.com/in/alex-allen-turl-07370146