Icons and text is not visibile on gdm3 greeter when two monitors attached

[ultrabit]

On my laptop when rebooting with attached external monitor, icons and text disappear from the gdm3 greeter (as in the picture in attachment).

This issue does not occur when rebooting using only one monitor.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: gdm3 3.28.0-0ubuntu1
ProcVersionSignature: Ubuntu 4.15.0-15.16-generic 4.15.15
Uname: Linux 4.15.0-15-generic x86_64
ApportVersion: 2.20.9-0ubuntu4
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Sun Apr 15 10:19:53 2018
InstallationDate: Installed on 2018-02-27 (46 days ago)
InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Alpha amd64 (20180227)
SourcePackage: gdm3
UpgradeStatus: No upgrade log present (probably fresh install)