Steps to reproduce:

1. Install clean installation of Ibexa DXP 4.4
2. Add some contents to the content tree
3. Set some of them as bookmark
4. Check the Doctrine tab in the Symfony Profiler for .../api/ibexa/v2/location/tree/load-subtree request

Result:

Many queries of the type (in the customer's case 814 queries) 

SELECT id, name, user_id, node_id FROM ezcontentbrowsebookmark WHERE (user_id = :user_id) AND (node_id IN (:location_id));

Bookmarks don't seem to be cached

Expected result:

Bookmarks should be cached