[PLASMA 5] KDE crashes

[Guest]

My Kubuntu

 cat /etc/issue
Ubuntu 16.04.1 LTS \n \l

Sometimes crashes without any visible reason
First problem is KWin crash, windows borders and headers just dissapears.. impossble switch or drag windows after.
Second problem wi-fi crashes sometimes network-manager says not network.. or speed arount 150k/sec.. (usually in normal state about 1M/sec) reboot helps and works until first hibernate, after situation quite the same.
Seems like hardware problem. But in the latest openSuse KDE works like a charm.. no crashes.. wi-fi always fine.
Resent problem with kernel update 4.4.0-28-generic this one works, but linux-image-4.4.0-31-generic this one just starting flashing CapsLock led just after GRUB and 'Kubuntu' logo on the screen.. and stop on this stage. no reaction on any key.
Any suggestions how to investigate and fix this?
Which log file I should inpect. in Xorg.0.log everything seems fine not errors.
dmesg tails

[ 1648.532278] IPv6: ADDRCONF(NETDEV_CHANGE): wlx00c0ca7b7c1a: link becomes ready
[ 1648.555484] cfg80211: Regulatory domain changed to country: GB
[ 1648.555487] cfg80211: DFS Master region: ETSI
[ 1648.555489] cfg80211: (start_freq - end_freq @ bandwidth), (max_antenna_gain, max_eirp), (dfs_cac_time)
[ 1648.555491] cfg80211: (2402000 KHz - 2482000 KHz @ 40000 KHz), (N/A, 2000 mBm), (N/A)
[ 1648.555493] cfg80211: (5170000 KHz - 5250000 KHz @ 80000 KHz, 160000 KHz AUTO), (N/A, 2000 mBm), (N/A)
[ 1648.555494] cfg80211: (5250000 KHz - 5330000 KHz @ 80000 KHz, 160000 KHz AUTO), (N/A, 2000 mBm), (0 s)
[ 1648.555496] cfg80211: (5490000 KHz - 5710000 KHz @ 160000 KHz), (N/A, 2700 mBm), (0 s)
[ 1648.555497] cfg80211: (57000000 KHz - 66000000 KHz @ 2160000 KHz), (N/A, 4000 mBm), (N/A)
[ 8345.904380] [drm:intel_pipe_update_end [i915]] *ERROR* Atomic update failure on pipe B (start=500651 end=500652) time 75 us, min 1073, max 1079, scanline start 1060, end 1080

kwin crash dmesg just after

[ 9840.816776] cfg80211: (2402000 KHz - 2472000 KHz @ 40000 KHz), (N/A, 2000 mBm), (N/A)
[ 9840.816778] cfg80211: (2457000 KHz - 2482000 KHz @ 40000 KHz), (N/A, 2000 mBm), (N/A)
[ 9840.816780] cfg80211: (2474000 KHz - 2494000 KHz @ 20000 KHz), (N/A, 2000 mBm), (N/A)
[ 9840.816783] cfg80211: (5170000 KHz - 5250000 KHz @ 80000 KHz, 160000 KHz AUTO), (N/A, 2000 mBm), (N/A)
[ 9840.816786] cfg80211: (5250000 KHz - 5330000 KHz @ 80000 KHz, 160000 KHz AUTO), (N/A, 2000 mBm), (0 s)
[ 9840.816788] cfg80211: (5490000 KHz - 5730000 KHz @ 160000 KHz), (N/A, 2000 mBm), (0 s)
[ 9840.816790] cfg80211: (5735000 KHz - 5835000 KHz @ 80000 KHz), (N/A, 2000 mBm), (N/A)
[ 9840.816792] cfg80211: (57240000 KHz - 63720000 KHz @ 2160000 KHz), (N/A, 0 mBm), (N/A)
[ 9848.387828] bbswitch: disabling discrete graphics
[ 9848.387840] ACPI Warning: \_SB_.PCI0.PEG0.GFX0._DSM: Argument #4 type mismatch - Found [Buffer], ACPI requires [Package] (20150930/nsarguments-95)

My laptop uses Nvidea 610 video card with Optimus. Driver from bumblebee quite standard. But the same crashes appears even on default installation!

mf@mf-laptop:~$ dpkg --list | grep bumblebee
ii bumblebee 3.2.1-10 amd64 NVIDIA Optimus support for Linux
ii bumblebee-nvidia 3.2.1-10 amd64 NVIDIA Optimus support using the proprietary NVIDIA driver
mf@mf-laptop:~$ plasmashell -v
plasmashell 5.5.5

[acheron]

What version of plasma are you running?

5.5.5 or 5.6.5?

plasmashell -v

[Guest]

First one.

[acheron]

Well, for starters most people are finding Plasma 5.6.5 from ppa:kubuntu-ppa/backports to quicker and more stable.

It is a backport though, and not an official 'stable' update, so use at own risk.