In plasma5 the work space freezes for a period intermittently and journalctl
has this output:
Jul 24 10:14:49 arbuthnot kernel: [drm] GPU HANG: ecode 6:0:0xbd73ffff, in
plasmashell [3124], reason: Hang on render ring, action: reset
Jul 24 10:14:49 arbuthnot kernel: [drm] GPU hangs can indicate a bug anywhere
in the entire gfx stack, including userspace.
Jul 24 10:14:49 arbuthnot kernel: [drm] Please file a _new_ bug report on
bugs.freedesktop.org against DRI -> DRM/Intel
Jul 24 10:14:49 arbuthnot kernel: [drm] drm/i915 developers can then reassign
to the right component if it's not a kernel issue.
Jul 24 10:14:49 arbuthnot kernel: [drm] The gpu crash dump is required to
analyze gpu hangs, so please always attach it.
Jul 24 10:14:49 arbuthnot kernel: [drm] GPU crash dump saved to
/sys/class/drm/card0/error
Jul 24 10:14:49 arbuthnot kernel: drm/i915: Resetting chip after gpu hang

Sometimes it can occur continuously but ctl-alt-f1 to a console and init 3 is
still possible.
This is after a zypper dup --no-allow-vendor-change from 42.2 where this
problem didn't occur.
Setting nomodeset at boot makes the problem go away.
My graphics is :
08: PCI 02.0: 0300 VGA compatible controller (VGA)              
  [Created at pci.378]
  Unique ID: _Znp.Ek_1fzLhuA5
  SysFS ID: /devices/pci0000:00/0000:00:02.0
  SysFS BusID: 0000:00:02.0
  Hardware Class: graphics card
  Model: "Intel 2nd Generation Core Processor Family Integrated Graphics
Controller"
  Vendor: pci 0x8086 "Intel Corporation"
  Device: pci 0x0102 "2nd Generation Core Processor Family Integrated Graphics
Controller"
  SubVendor: pci 0x105b "Foxconn International, Inc."
  SubDevice: pci 0x0d8d 
  Revision: 0x09
  Memory Range: 0xf7800000-0xf7bfffff (rw,non-prefetchable)
  Memory Range: 0xe0000000-0xefffffff (ro,non-prefetchable)
  I/O Ports: 0xf000-0xf03f (rw)
  IRQ: 11 (no events)
  I/O Ports: 0x3c0-0x3df (rw)
  Module Alias: "pci:v00008086d00000102sv0000105Bsd00000D8Dbc03sc00i00"
  Driver Info #0:
    Driver Status: i915 is active
    Driver Activation Cmd: "modprobe i915"
  Config Status: cfg=no, avail=yes, need=no, active=unknown

Primary display adapter: #8

My cpu is an "Intel(R) Core(TM) i3-2120 CPU @ 3.30GHz"