Screen automatically relocks a few seconds after being unlocked

Iḿ using Ubuntu 18.04 beta 2, with Dash to panel extension (don't know if it has any relevance to the issue, but whatever). Very often (but not always) when I lock the screen and try to login after some time, the screen is unlocked like it should be, but a few seconds later the screen is locked again. Sometimes I have to login 5 or 6 times until this issue stops happening, and sometimes my session is destroyed and all my opened programs are closed.

I've setted the screen to turn off after 10 minutes in Energy Settings (again, I don't know if this has any relevance).

gdm3 version: 3.28.0-0ubuntu1

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: gnome-screensaver (not installed)
ProcVersionSignature: Ubuntu 4.15.0-15.16-generic 4.15.15
Uname: Linux 4.15.0-15-generic x86_64
ApportVersion: 2.20.9-0ubuntu5
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Thu Apr 19 14:42:35 2018
InstallationDate: Installed on 2018-04-12 (7 days ago)
InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Beta amd64 (20180404)
SourcePackage: gnome-screensaver
UpgradeStatus: No upgrade log present (probably fresh install)