Two servers, different OC versions

Please help us by providing the following info. Before posting please also check the pinned "Known issues" threads and make sure that you're running the latest available version for your oC release:

Steps to reproduce
1.set up 2 different servers. Both servers started from before 9.0.x
2. upgrade both servers in the correct order to 9.0.x
3. One server stops auto upgrade at 9.0.5 and other server is at 9.1.5

Expected behaviour
Both servers should be at 9.1.5

Actual behaviour
One server is stuck on 9.0.x

Server configuration
Operating system: Both servers at Ubuntu 14.04.5
Web server: Apache 2.4 (both)
Database: MySql 5.5.55 (both)
PHP version: 5.6.23 (stuck at 9.0.x), 5.5.0 (upgraded to 9.1.x)
ownCloud version (see ownCloud admin page):
Updated from an older ownCloud or fresh install: Upgraded
Special configuration (external storage, external authentication, reverse proxy, server-side-encryption):

ownCloud configuration

ownCloud log (data/owncloud.log)

Integrity status for oC9+

No errors have been found.

There are no auto-updates in ownCloud so its up to you (or your admin) to roll out the updates and upgrades.

I guess I should have been more specific. I am sorry.

When I run the command "sudo -u apache php occ upgrade". One server says that 9.0.5 is the most current version, the other server upgrades to 9.1.5.

occ upgrade won't do the update/upgrade of oC for you (it only runs the database upgrade routine after you have updated to ownCloud code).

To upgrade this instance you need to do the following steps:

9.0.5 -> latest 9.0.x -> latest 9.1.x

by following the steps provided here:
-> If you have done a manual installation
-> If you had used the repositories