Search suggestions don't work anymore in 16.3.0 in private wikis as the configuration cannot be accessed in the webjar resource handler as it has no authenticated user. See also XWIKI-22147. This is a duplicate of XWIKI-22147 to track the development of a proper fix for 16.4.0RC1 while XWIKI-22147 has been closed with a revert for 16.3.1.