can't maximise in one monitor

[nicolas]

I have a dual monitor setup. Sometimes, when I log back in from the lock screen (I mean the session is already running), one of the screens does something quite strange. When I try maximise a window, it only uses a small part of the screen's width, as you can see here https://ibb.co/epueGd
I also can't drag the right border of a window to make it bigger. The left border works fine. The only solution I've found is to go to system settings-> displays, disable one of the monitors, and then enabling it again. Logging out and back in, doesn't help.
I suppose it is an xorg related bug, sorry if it's not.

information:

1) Description: Ubuntu 16.04.4 LTS
Release: 16.04

2) xorg:
  Installed: 1:7.7+13ubuntu3
  Candidate: 1:7.7+13ubuntu3
  Version table:
 *** 1:7.7+13ubuntu3 500
        500 http://ar.archive.ubuntu.com/ubuntu xenial/main amd64 Packages
        100 /var/lib/dpkg/status

3) Expected: window is maximised normally.

4) What happens: It only uses a portion of the width.

PS:
Here's the screenshot again, in case the other one fails.
https://photos.app.goo.gl/sdh37ktA8nCAHAum6

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: xorg 1:7.7+13ubuntu3
ProcVersionSignature: Ubuntu 4.13.0-45.50~16.04.1-generic 4.13.16
Uname: Linux 4.13.0-45-generic x86_64
NonfreeKernelModules: wl
.tmp.unity_support_test.0:

ApportVersion: 2.20.1-0ubuntu2.18
Architecture: amd64
CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins'
CompositorRunning: compiz
CompositorUnredirectDriverBlacklist: '(nouveau|Intel).*Mesa 8.0'
CompositorUnredirectFSW: true
CurrentDesktop: Unity
Date: Thu Jul 5 13:16:07 2018
DistUpgraded: Fresh install
DistroCodename: xenial
DistroVariant: ubuntu
EcryptfsInUse: Yes
ExtraDebuggingInterest: Yes
GraphicsCard:
 Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller [8086:0102] (rev 09) (prog-if 00 [VGA controller])
   Subsystem: Lenovo 2nd Generation Core Processor Family Integrated Graphics Controller [17aa:307b]
InstallationDate: Installed on 2018-05-18 (48 days ago)
InstallationMedia: Ubuntu 16.04.4 LTS "Xenial Xerus" - Release amd64 (20180228)
MachineType: LENOVO 1782A2Y
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.13.0-45-generic root=UUID=5cac15b6-1f9d-412c-ab2c-2f9318328d66 ro quiet splash vt.handoff=7
SourcePackage: xorg
Symptom: display
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 08/23/2011
dmi.bios.vendor: LENOVO
dmi.bios.version: 9PKT26AUS
dmi.board.asset.tag: To be filled by O.E.M.
dmi.board.name: To be filled by O.E.M.
dmi.board.vendor: LENOVO
dmi.board.version: To be filled by O.E.M.
dmi.chassis.type: 3
dmi.chassis.vendor: To Be Filled By O.E.M.
dmi.chassis.version: To Be Filled By O.E.M.
dmi.modalias: dmi:bvnLENOVO:bvr9PKT26AUS:bd08/23/2011:svnLENOVO:pn1782A2Y:pvrThinkCentreM71z:rvnLENOVO:rnTobefilledbyO.E.M.:rvrTobefilledbyO.E.M.:cvnToBeFilledByO.E.M.:ct3:cvrToBeFilledByO.E.M.:
dmi.product.family: To be filled by O.E.M.
dmi.product.name: 1782A2Y
dmi.product.version: ThinkCentre M71z
dmi.sys.vendor: LENOVO
version.compiz: compiz 1:0.9.12.3+16.04.20180221-0ubuntu1
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.83-1~16.04.1
version.libgl1-mesa-dri: libgl1-mesa-dri 17.2.8-0ubuntu0~16.04.1
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 17.2.8-0ubuntu0~16.04.1
version.xserver-xorg-core: xserver-xorg-core N/A
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev N/A
version.xserver-xorg-video-ati: xserver-xorg-video-ati N/A
version.xserver-xorg-video-intel: xserver-xorg-video-intel N/A
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau N/A
xserver.bootTime: Fri Jun 29 00:13:48 2018
xserver.configfile: default
xserver.devices:
 input Power Button KEYBOARD, id 6
 input Power Button KEYBOARD, id 7
 input Integrated Camera: Integrated C KEYBOARD, id 8
 input Lenovo Optical USB Mouse MOUSE, id 9
 input CHICONY USB NetVista Full Width Keyboard KEYBOARD, id 10
xserver.errors:

xserver.logfile: /var/log/Xorg.0.log
xserver.version: 2:1.19.5-0ubuntu2~16.04.1
xserver.video_driver: modeset