I recently attempted upgrading my ownCloud instance from 8.0.2 to 9.1.0. The main problem I ran into was that users could not see external storage that I had set up for one of our NAS servers, even though I had added back all of the shares in the External Storage Support plugin. Using the "Log-in Credentials, save-in session" would not work at all; nor would "User name and password" pointing to a domain admin account. User A logs in, can see their shares, but when they click on a share, it throws an error: "Storage not available." I ended up having to rollback my snapshot to 8.0.2 prevent work stoppage.
Any thoughts or ideas?