We've relocated the Import CSV button and all associated functionality into the Import history tab of the address book:

Clicking on the "Import history" tab will show a list of all previous CSV imports (if applicable) and enable the "Import new CSV" button. Additional details on CSV import workflows and file format requirements can be found here.

Click the eye icon to the right of any previous CSV import to view a list of stops that are associated with that imported CSV:

From here, click "Add all to custom stops" to migrate the imported data from this CSV into the Custom stops tab of the address book for quick addition to routes: