There can be several reasons for this. One of them might be that you are not running the maintenance plans on the EV databases. See https://www.veritas.com/support/en_US/article.100022023.html for how to. Check with your DBA on this.
To check the amount of deleted items, see https://www.veritas.com/support/en_US/article.100039333.html
This has a query you can run against the vault store. If you run it once every two hours, the count should go down.
It might also be that there is an issue on the index server(s), check EV eventlog for obvious alerts (failed to remove etc.)
As you are on EV11, try to go to 11.0.1 CHF5, which is the latest 11 version. If possible, then upgrade to 12.3, so you get the latest possible version.