We too are on prem, v9.1.1, and are having issues with Auto Update. The console itself shows 'update pushed', and I do see a notification in the top right stating 'the AirWatch Agent app has been updated to the latest version', which is from 8/18/2018, right around the time of v.5.8. Unfortunately, we have huge numbers of devices (all iOS) in our environment, that are connected to the Internet via LTE and do not have the updated app, in our case, the AirWatch Agent, v.5.8. Some are my test devices, and they are fully connected to the console, APNs working properly, etc. We've had VPP set up for a couple months, so our Auto-Update was there prior to 5.8 being released. I've spot checked many of the devices and can hover over the 'install' check mark for Agent and see that it is managed as well.
I did read a support article that states ' iOS devices cannot process an application install when it is locked.' This shouldn't apply in my case as mine are on and open. I'm going to submit a ticket to AW Support and I'll keep you posted. We are also moving to the latest on-prem version in a few months, so maybe we'll have better luck then.