I have an iPhone that is enrolled via DEP, and using settings that include supervision. If I wipe the iPhone and restore from iCloud, the phone is not supervised, even though the DEP screen shows the settings pushed at the appropriate time.
I've seen that happen to a phone or two at my workplace too. I found it seems to be caused by restoring from an iCloud backup. It only happened with two phones, so there might've been something weird with those phone backups or configurations. I've been able to restore from iCloud and supervise any other time without issue. I couldn't figure out why it wouldn't work those two times though.
What I ended up doing was to setup the phone as new, but restored the data through a free app named "CopyMyData". It's not as good as an iCloud backup/restore, but it transfers most of the important stuff.
From my understanding, if you use DEP the device should become supervised by any means, even if an unsupervised backup is applied. Is your Meraki Management Profile locked on the device - if so, the device is supervised?
I had a user who had an unsupervised backup on iTunes on their computer. I went through setup, signing in with his AD creds to start enrollment and then plugged into iTunes and restored, seems to be working for us.
I've tried this multiple ways, multiple times. Installing as a new phone gets it supervised, but restoring either from iCloud or iTunes, then it's not supervised. In all cases, the date and time on the DEP screen indicates settings were pushed.
Interesting. I just restored the same backup that didn't work onto a different phone (iPhone 6s this time, vs. iPhone 8 before) and it is supervised.
So, on the phone that didn't work, I removed the SM app, removed management, made a new backup, then erased the phone again. Still didn't work. Maybe this issue is specific to iPhone 8?