This appears to be a problem with Airwatch. I had this issue and have spoken to a few people from other companies that are experiencing this issue.
What I found was the security profile that was being applied was causing this issue (confirmed by going into the Agent on the phone, then Profiles, selected the security profile and clicked re-apply). Once clicking re-apply the NavBar would appear again for a second then disappear again.
I removed the security profile altogether and lo and behold the NavBar was back again. Manually pushed the security profile down from the AW Console to my device and it has been working since.