We've recently added caching to our server and it may be causing problems with LDAP. Users can successfully login to owncloud, but when you issue the following command: "sudo -u apache php occ ldap:check-user validuser
The user does not exists on LDAP anymore. (If we search for this user in the LDAP GUI, it shows up as valid)
We tried updating from 8.2.9 to 8.2.11, but that didn't fix the problem. We also tried using --force with the command and that didn't help wither. This problem is also causing issues with shared files. Please let us know if you have questions.