I had the same problem:

Nov  5 10:56:01 daniel-Inspiron-3543 kernel: [ 8431.056748] nouveau
0000:05:00.0: fifo: SCHED_ERROR 0a [CTXSW_TIMEOUT]
Nov  5 10:56:01 daniel-Inspiron-3543 kernel: [ 8431.056765] nouveau
0000:05:00.0: fifo: runlist 0: scheduled for recovery
Nov  5 10:56:01 daniel-Inspiron-3543 kernel: [ 8431.056781] nouveau
0000:05:00.0: fifo: channel 15: killed
Nov  5 10:56:01 daniel-Inspiron-3543 kernel: [ 8431.056791] nouveau
0000:05:00.0: fifo: engine 7: scheduled for recovery
Nov  5 10:56:01 daniel-Inspiron-3543 kernel: [ 8431.056798] nouveau
0000:05:00.0: fifo: engine 0: scheduled for recovery
Nov  5 10:56:01 daniel-Inspiron-3543 kernel: [ 8431.057508] nouveau
0000:05:00.0: gnome-shell[4200]: channel 15 killed!

lsb_release -d
Description:    Ubuntu 18.04.1 LTS
gnome-shell --version
GNOME Shell 3.28.3

sudo lshw -c video
  *-display                 
       description: VGA compatible controller
       product: GK107 [NVS 510]
       vendor: NVIDIA Corporation
       physical id: 0
       bus info: pci@0000:05:00.0
       version: a1
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress vga_controller bus_master cap_list rom
       configuration: driver=nouveau latency=0
       resources: irq:47 memory:de000000-deffffff memory:c0000000-cfffffff
memory:d0000000-d1ffffff ioport:c000(size=128) memory:c0000-dffff

hwinfo --gfxcard
56: PCI 500.0: 0300 VGA compatible controller (VGA)             
  [Created at pci.378]
  Unique ID: Ddhb.WEoD030yuUF
  Parent ID: _Znp.jlvukYYcj4B
  SysFS ID: /devices/pci0000:00/0000:00:02.0/0000:05:00.0
  SysFS BusID: 0000:05:00.0
  Hardware Class: graphics card
  Model: "nVidia GK107 [NVS 510]"
  Vendor: pci 0x10de "nVidia Corporation"
  Device: pci 0x0ffd "GK107 [NVS 510]"
  SubVendor: pci 0x10de "nVidia Corporation"
  SubDevice: pci 0x0967 
  Revision: 0xa1
  Driver: "nouveau"
  Driver Modules: "nouveau"
  Memory Range: 0xde000000-0xdeffffff (rw,non-prefetchable)
  Memory Range: 0xc0000000-0xcfffffff (ro,non-prefetchable)
  Memory Range: 0xd0000000-0xd1ffffff (ro,non-prefetchable)
  I/O Ports: 0xc000-0xc07f (rw)
  Memory Range: 0x000c0000-0x000dffff (rw,non-prefetchable,disabled)
  IRQ: 47 (296925 events)
  I/O Port: 0x00 (rw)
  Module Alias: "pci:v000010DEd00000FFDsv000010DEsd00000967bc03sc00i00"
  Driver Info #0:
    Driver Status: nvidiafb is not active
    Driver Activation Cmd: "modprobe nvidiafb"
  Driver Info #1:
    Driver Status: nouveau is active
    Driver Activation Cmd: "modprobe nouveau"
  Config Status: cfg=new, avail=yes, need=no, active=unknown
  Attached to: #73 (PCI bridge)

Primary display adapter: #56