I've spent the morning testing with this
Created a ADE profile with a 5GB
NO Authentication
Wiped device
Ensured I had a bunch of users in school.apple.com
Used my existing Education profile, which includes a device group to aid logging in:
Synced Users from Systems Manager > Overview∫
Synced Users from the top of the Education profile above
Wiped device and enrolled
Got to logging in, which I did with three users
No issues.
I'd look at your quote size. This is in MB, not GB, so my 5000 above is just shy of 5GB
I hope that helps