The issue was seen when installing the latest CU. When installing the SQL part of a cumulative update you get the error:-
Install-CsDatabase : Command execution failed: Cannot find any suitable disks for database files. You must manually specify database paths.
The “suitable disks” error is triggered by the installer checks. The requirement is that a minimum of 16 GB of free space is available prior to installingupdating SQL. Simply cleaning up the drive where CSDATA lives to free up space gets it sorted.