Description of problem:
Recent gdm update (gdm 1:3.28.3-1.fc28) results in failed login

Version-Release number of selected component (if applicable):
gdm 1:3.28.3-1.fc28

How reproducible:
Always

Steps to Reproduce:
1.Took Virtualbox Fedora 28 VM snapshot, then logged in and ran 'sudo dnf upgrade' and checked the list of packages to be updated, which included gdm 1:3.28.3-1.fc28
2.After logging out, cannot log back in - after password entered, login fails and returns to login screen (same result either as regular or root user)
3. Restored Virtualbox Fedora 28 VM to snapshot, then logged in and ran 'sudo dnf upgrade --exclude gdm', then logged out and no problem logging back in after that.

Actual results:
Failed login with infinite futile login screen loop

Expected results:
Trouble-free upgrade with no problem logging in.

Additional info:
Cannot update gdm (3.28.2) on Fedora 28 until this bug is fixed