When I try to add an existing user to a site, the search query for user from Site Management section returns only the default Administrator user, although there are several other users added in alfresco (the sample ones from the sample site and also the ones synchronized from AD).
The AD users can login into alfresco.
No error is found in logs.
Also, when the search is done as administrator from Admin Tools > Users page, all users are returned.
Now the details:
Alfresco Community 6.1 using Tomcat 8, NginX, Postgresql11 on CentOS8