Hi all,
interesting issue I've just faced:
Upgrade to EV 10 SP3, after upgrade of directory DB and storage DB, I started the Index service and got the following error:
Event 41312 : The Indexing Service could not complete all the required startup routines: Enterprise Vault Server Cache is not configured for this computer. Service will be stopped.
since index service is not working, I bypassed the issue by doing the following:
Logged in to SQL, opened ComputerEntry db (from EnterpriseVaultDirectory) in edit mode, and entered cache location manually.
Closed SQL, started indexing service - came up and continued with Indexing upgrade 
FYI.
BTW - I know for sure that this issue did not accrue in upgrade to EV 10 SP1.
Would consider adding the cache location issue to the deployment scanner so it will alert prior to the upgrade...
Sarah.