Hi!
What you described rings a bell to me, making me thing about something that happened to several people I’ve seen using the Owncloud Rock-on. Could you confirm what version of Owncloud Rock-on you installed? The one named simply “Rock-on”?
If yes, I would recommend other version available as Rock-on, or even the Nextcloud one. This is due to the fact that the “Owncloud” has not been updated in a while and is now several versions behind as far as I remember.
If you still prefer to use the Owncloud you already installed, you should have a look at the following post, or search in this forum for a problem with localtime in this Rock-on.