plymouth-start.service: Job plymouth-start.service/start deleted to break ordering cycle starting with plymouth-quit-wait.service/start

[dino99]

plymouth ends with that error:

systemd[1]: plymouth-quit-wait.service: Found ordering cycle on plymouth-quit-wait.service/start
systemd[1]: plymouth-quit-wait.service: Found dependency on plymouth-start.service/start
systemd[1]: plymouth-quit-wait.service: Found dependency on keyboard-setup.service/start
systemd[1]: plymouth-quit-wait.service: Found dependency on plymouth-quit-wait.service/start
systemd[1]: plymouth-quit-wait.service: Breaking ordering cycle by deleting job plymouth-start.service/start
systemd[1]: plymouth-start.service: Job plymouth-start.service/start deleted to break ordering cycle starting with plymouth-quit-wait.service/start

but the booting processes can continue, and finally load X with difficulties (lot of delay and hdd scanning)

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: plymouth 0.9.2-3ubuntu13.1
ProcVersionSignature: Ubuntu 4.4.0-25.44-generic 4.4.13
Uname: Linux 4.4.0-25-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia_modeset nvidia
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
BootLog:

CurrentDesktop: GNOME
Date: Sat Jun 18 10:52:36 2016
DefaultPlymouth: /usr/share/plymouth/themes/ubuntu-logo/ubuntu-logo.plymouth
Lsusb:
 Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
 Bus 003 Device 002: ID 046d:c062 Logitech, Inc. M-UAS144 [LS1 Laser Mouse]
 Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
 Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
MachineType: ASUSTEK COMPUTER INC P5W DH Deluxe
ProcCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.4.0-25-generic root=UUID=dec5c521-a4b3-44f9-af5c-a23fb12227ff ro
ProcFB:

ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.4.0-25-generic root=UUID=dec5c521-a4b3-44f9-af5c-a23fb12227ff ro
SourcePackage: plymouth
TextPlymouth: /usr/share/plymouth/themes/ubuntu-text/ubuntu-text.plymouth
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 07/22/2010
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 3002
dmi.board.asset.tag: To Be Filled By O.E.M.
dmi.board.name: P5W DH Deluxe
dmi.board.vendor: ASUSTeK Computer INC.
dmi.board.version: Rev 1.xx
dmi.chassis.asset.tag: Asset-1234567890
dmi.chassis.type: 3
dmi.chassis.vendor: Chassis Manufacture
dmi.chassis.version: Chassis Version
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr3002:bd07/22/2010:svnASUSTEKCOMPUTERINC:pnP5WDHDeluxe:pvrSystemVersion:rvnASUSTeKComputerINC.:rnP5WDHDeluxe:rvrRev1.xx:cvnChassisManufacture:ct3:cvrChassisVersion:
dmi.product.name: P5W DH Deluxe
dmi.product.version: System Version
dmi.sys.vendor: ASUSTEK COMPUTER INC