Graphics problems after running out of space

I am experiencing random graphics problems after I ran out of space (only one partition without considering swap) because I left overnight a very big download.
I have already recovered the space after deleting that big files, but in occasions ( I have not identified what triggers the probleml) the background windows are shown through the front ones. Minimize, restore, maximize, and moving windows stop working. That is, most of graphics elements become unresponsive. A reboot or logoff solves the problems until it starts again.
I am using Ubuntu 20.04 installed on hard disk using a LG 22M35D monitor. This is the output of the diagnostic command:

System:
  Host: Home Kernel: 5.8.0-49-generic x86_64 bits: 64 Desktop: Gnome 3.36.7
  Distro: Ubuntu 20.04.2 LTS (Focal Fossa)
Machine:
  Type: Desktop System: TSINGHUA TONGFANG product: H81M-CT v: N/A
  serial: <superuser/root required>
  Mobo: ASUSTeK model: H81M-CT v: Rev 1.00 serial: <superuser/root required>
  UEFI: American Megatrends v: A801AP0M date: 02/13/2015
CPU:
  Topology: Quad Core model: Intel Core i5-4590 bits: 64 type: MCP
  L2 cache: 6144 KiB
  Speed: 1166 MHz min/max: 800/3700 MHz Core speeds (MHz): 1: 1100 2: 1104
  3: 1110 4: 1105
Graphics:
  Device-1: Intel Xeon E3-1200 v3/4th Gen Core Processor Integrated Graphics
  driver: i915 v: kernel
  Display: x11 server: X.Org 1.20.9 driver: fbdev unloaded: modesetting,vesa
  resolution: 1920x1080~60Hz
  OpenGL: renderer: Mesa DRI Intel HD Graphics 4600 (HSW GT2)
  v: 4.5 Mesa 20.2.6
Audio:
  Device-1: Intel Xeon E3-1200 v3/4th Gen Core Processor HD Audio
  driver: snd_hda_intel
  Device-2: Intel 8 Series/C220 Series High Definition Audio
  driver: snd_hda_intel
  Sound Server: ALSA v: k5.8.0-49-generic
Network:
  Device-1: Realtek RTL8111/8168/8411 PCI Express Gigabit Ethernet
  driver: r8169
  IF: enp3s0 state: down mac: 14:dd:a9:7d:73:b5
  Device-2: Qualcomm Atheros AR9271 802.11n type: USB driver: ath9k_htc
  IF: wlxe894f6266a3d state: up mac: e8:94:f6:26:6a:3d
Drives:
  Local Storage: total: 1.82 TiB used: 19.89 GiB (1.1%)
  ID-1: /dev/sda vendor: Seagate model: ST2000DM001-1ER164 size: 1.82 TiB
Partition:
  ID-1: / size: 28.71 GiB used: 19.86 GiB (69.2%) fs: ext4 dev: /dev/sda6
Sensors:
  System Temperatures: cpu: 29.8 C mobo: 27.8 C
  Fan Speeds (RPM): N/A
Info:
  Processes: 222 Uptime: 28m Memory: 7.68 GiB used: 1.11 GiB (14.4%)
  Shell: bash inxi: 3.0.38

mode "1920x1080"
    geometry 1920 1080 1920 1080 32
    timings 0 0 0 0 0 0 0
    accel true
    rgba 8/16,8/8,8/0,0/0
endmode

Frame buffer device information:
    Name : i915drmfb
    Address : 0
    Size : 8294400
    Type : PACKED PIXELS
    Visual : TRUECOLOR
    XPanStep : 1
    YPanStep : 1
    YWrapStep : 0
    LineLength : 7680
    Accelerator : No
Version: 1:7.7+19ubuntu14
Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 16384 x 16384
VGA-1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 480mm x 270mm
   1920x1080 60.00*+
   1680x1050 59.95
   1400x1050 59.98
   1600x900 60.00
   1280x1024 75.02 60.02
   1440x900 59.89
   1280x800 59.81
   1152x864 75.00
   1280x720 60.00
   1024x768 75.03 60.00
   832x624 74.55
   800x600 75.00 60.32 56.25
   640x480 75.00 59.94
   720x400 70.08
HDMI-1 disconnected (normal left inverted right x axis y axis)
fglrxinfo: orden no encontrada

No se ha encontrado la orden «nvidia-settings», pero se puede instalar con:

sudo apt install nvidia-settings

ruta H/W Dispositivo Clase Descripción
===========================================================
                                system H81M-CT (All)
/0 bus H81M-CT
/0/0 memory 64KiB BIOS
/0/4 processor Intel(R) Core(TM) i5-4590 CPU @ 3
/0/4/5 memory 256KiB L1 caché
/0/4/6 memory 1MiB L2 caché
/0/4/7 memory 6MiB L3 caché
/0/1 memory 8GiB Memoria de sistema
/0/1/0 memory 4GiB DIMM DDR3 Síncrono 1600 MHz
/0/1/1 memory 4GiB DIMM DDR3 Síncrono 1600 MHz
/0/100 bridge 4th Gen Core Processor DRAM Contr
/0/100/1 bridge Xeon E3-1200 v3/4th Gen Core Proc
/0/100/2 display Xeon E3-1200 v3/4th Gen Core Proc
/0/100/3 multimedia Xeon E3-1200 v3/4th Gen Core Proc
/0/100/14 bus 8 Series/C220 Series Chipset Fami
/0/100/14/0 usb3 bus xHCI Host Controller
/0/100/14/0/4 input USB Mouse
/0/100/14/0/7 communication SAMSUNG_Android
/0/100/14/0/8 storage Mass Storage Device
/0/100/14/0/9 generic USB2.0 WLAN
/0/100/14/1 usb4 bus xHCI Host Controller
/0/100/16 communication 8 Series/C220 Series Chipset Fami
/0/100/1a bus 8 Series/C220 Series Chipset Fami
/0/100/1a/1 usb1 bus EHCI Host Controller
/0/100/1a/1/1 bus USB hub
/0/100/1b multimedia 8 Series/C220 Series Chipset High
/0/100/1c bridge 8 Series/C220 Series Chipset Fami
/0/100/1c.2 bridge 8 Series/C220 Series Chipset Fami
/0/100/1c.2/0 enp3s0 network RTL8111/8168/8411 PCI Express Gig
/0/100/1c.5 bridge 82801 PCI Bridge
/0/100/1c.5/0 bridge ASM1083/1085 PCIe to PCI Bridge
/0/100/1d bus 8 Series/C220 Series Chipset Fami
/0/100/1d/1 usb2 bus EHCI Host Controller
/0/100/1d/1/1 bus USB hub
/0/100/1f bridge H81 Express LPC Controller
/0/100/1f.2 storage 8 Series/C220 Series Chipset Fami
/0/100/1f.3 bus 8 Series/C220 Series Chipset Fami
/0/2 system PnP device PNP0c01
/0/3 system PnP device PNP0c02
/0/5 system PnP device PNP0b00
/0/6 generic PnP device INT3f0d
/0/7 system PnP device PNP0c02
/0/8 printer PnP device PNP0400
/0/9 system PnP device PNP0c02
/0/a communication PnP device PNP0501
/0/b communication PnP device PNP0501
/0/c input PnP device PNP0303
/0/d system PnP device PNP0c02
/0/e scsi0 storage
/0/e/0.0.0 /dev/sda disk 2TB ST2000DM001-1ER1
/0/e/0.0.0/1 /dev/sda1 volume 498MiB Windows NTFS volumen
/0/e/0.0.0/2 /dev/sda2 volume 99MiB Windows FAT volumen
/0/e/0.0.0/3 /dev/sda3 volume 15MiB reserved partition
/0/e/0.0.0/4 /dev/sda4 volume 97GiB Windows NTFS volumen
/0/e/0.0.0/5 /dev/sda5 volume 1736GiB Windows NTFS volumen
/0/e/0.0.0/6 /dev/sda6 volume 29GiB partición EXT4
/0/f scsi4 storage
/0/f/0.0.0 /dev/sdb disk Flash Reader
/0/f/0.0.0/0 /dev/sdb disk
/1 power To Be Filled By O.E.M.
/2 wlxe894f6266a3d network Interfaz inalámbrica
  *-display
       descripción: VGA compatible controller
       producto: Xeon E3-1200 v3/4th Gen Core Processor Integrated Graphics Controller
       fabricante: Intel Corporation
       id físico: 2
       información del bus: pci@0000:00:02.0
       versión: 06
       anchura: 64 bits
       reloj: 33MHz
       capacidades: msi pm vga_controller bus_master cap_list rom
       configuración: driver=i915 latency=0
       recursos: irq:32 memoria:f7800000-f7bfffff memoria:e0000000-efffffff ioport:f000(size=64) memoria:c0000-dffff
ii gir1.2-ibus-1.0:amd64 1.5.22-2ubuntu2.1 amd64 Intelligent Input Bus - introspection data
ii i965-va-driver:amd64 2.4.0-0ubuntu1 amd64 VAAPI driver for Intel G45 & HD Graphics family
ii ibus 1.5.22-2ubuntu2.1 amd64 Intelligent Input Bus - core
ii ibus-data 1.5.22-2ubuntu2.1 all Intelligent Input Bus - data files
ii ibus-gtk:amd64 1.5.22-2ubuntu2.1 amd64 Intelligent Input Bus - GTK2 support
ii ibus-gtk3:amd64 1.5.22-2ubuntu2.1 amd64 Intelligent Input Bus - GTK3 support
ii intel-media-va-driver:amd64 20.1.1+dfsg1-1 amd64 VAAPI driver for the Intel GEN8+ Graphics family
ii intel-microcode 3.20201110.0ubuntu0.20.04.2 amd64 Processor microcode firmware for Intel CPUs
ii iucode-tool 2.3.1-1 amd64 Intel processor microcode tool
ii libdrm-intel1:amd64 2.4.102-1ubuntu1~20.04.1 amd64 Userspace interface to intel-specific kernel DRM services -- runtime
ii libdrm-nouveau2:amd64 2.4.102-1ubuntu1~20.04.1 amd64 Userspace interface to nouveau-specific kernel DRM services -- runtime
ii libdrm-radeon1:amd64 2.4.102-1ubuntu1~20.04.1 amd64 Userspace interface to radeon-specific kernel DRM services -- runtime
ii libegl-mesa0:amd64 20.2.6-0ubuntu0.20.04.1 amd64 free implementation of the EGL API -- Mesa vendor library
ii libgl1-mesa-dri:amd64 20.2.6-0ubuntu0.20.04.1 amd64 free implementation of the OpenGL API -- DRI modules
ii libglapi-mesa:amd64 20.2.6-0ubuntu0.20.04.1 amd64 free implementation of the GL API -- shared library
ii libglu1-mesa:amd64 9.0.1-1build1 amd64 Mesa OpenGL utility library (GLU)
ii libglx-mesa0:amd64 20.2.6-0ubuntu0.20.04.1 amd64 free implementation of the OpenGL API -- GLX vendor library
ii libibus-1.0-5:amd64 1.5.22-2ubuntu2.1 amd64 Intelligent Input Bus - shared library
ii libigdgmm11:amd64 20.1.1+ds1-1 amd64 Intel Graphics Memory Management Library -- shared library
ii mesa-utils 8.4.0-1build1 amd64 Miscellaneous Mesa GL utilities
ii mesa-va-drivers:amd64 20.2.6-0ubuntu0.20.04.1 amd64 Mesa VA-API video acceleration drivers
ii mesa-vdpau-drivers:amd64 20.2.6-0ubuntu0.20.04.1 amd64 Mesa VDPAU video acceleration drivers
ii mesa-vulkan-drivers:amd64 20.2.6-0ubuntu0.20.04.1 amd64 Mesa Vulkan graphics drivers
ii python3-ibus-1.0 1.5.22-2ubuntu2.1 all Intelligent Input Bus - introspection overrides for Python (Python 3)
ii xserver-xorg-video-ati 1:19.1.0-1 amd64 X.Org X server -- AMD/ATI display driver wrapper
ii xserver-xorg-video-intel 2:2.99.917+git20200226-1 amd64 X.Org X server -- Intel i8xx, i9xx display driver
ii xserver-xorg-video-nouveau 1:1.0.16-1 amd64 X.Org X server -- Nouveau display driver
ii xserver-xorg-video-radeon 1:19.1.0-1 amd64 X.Org X server -- AMD/ATI Radeon display driver
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=20.04
DISTRIB_CODENAME=focal
DISTRIB_DESCRIPTION="Ubuntu 20.04.2 LTS"
[ 0.000000] Intel GenuineIntel
[ 0.022805] Reserving Intel graphics memory at [mem 0xdd200000-0xdf1fffff]
[ 0.089194] smpboot: CPU0: Intel(R) Core(TM)