Cannot upgrade from 16.04.4 to 18.10

[Kherim Willems]

Original install is Ubuntu Server 16.04.1 with Cinnamon as GUI.
Currently running on kernel 4.16.2.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:16.04.25
Uname: Linux 4.16.2-041602-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia_drm nvidia_modeset nvidia
ApportVersion: 2.20.1-0ubuntu2.16
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: X-Cinnamon
Date: Fri Apr 13 16:55:25 2018
InstallationDate: Installed on 2016-10-28 (531 days ago)
InstallationMedia: Ubuntu-Server 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to xenial on 2018-04-13 (0 days ago)
VarLogDistupgradeTermlog:

mtime.conffile..etc.update-manager.release-upgrades: 2018-01-12T10:42:07.348791

[Jean-Baptiste Lallement (jibel)]

Thanks for your report.

You have package from non-official repositories installed which are blocking the upgrade.

In particular python3.6:

libpython3.6 3.6.3-1+xenial2 LP-PPA-thomas-schiex-blender
libpython3.6-minimal 3.6.3-1+xenial2 LP-PPA-thomas-schiex-blender
libpython3.6-stdlib 3.6.3-1+xenial2 LP-PPA-thomas-schiex-blender

which is not in Xenial.

Please uninstall these packages before upgrading again or revert to a version from the official Ubuntu repository.

I'm closing this report. Don't hesitate to file any bug you may find.