After a little research, I found this ownCloud GitHub issue: LDAPs lost connection, LDAP works. Try to see if it refers to the same problem that you are facing. If you correctly followed the ownCloud configuration and it keeps failing, I would try to debug the issue in the LDAP server side. Also,try to make requests to the server with a different client than ownCloud.
Hope it helps.
Note that this community forum is intended to solve problems related to the Bitnami Stacks, Virtual Machine or Cloud Images. For information regarding the application itself or customization of the content within the application, we always recommend checking forums and user guides made available by the project behind the application where you will find more appropriate contents and support about that matter.