ubuntu 20.04: green lines in background + crash at standby after upgrade

Question

I experience several odd errors and glinces after upgrading from ubuntu 18.04 to 20.04.

The first thing, I noticed were the funny green pixeled lines on the background wallpaper. They can be overlayed by windows and disappear when switching to a different image but remain on the original image, when switching back. This is also the case for other background images from the standard stock).

Further -- and much more annoying -- is that ubuntu repeatedly crashes at standby/when suspended, e.g. when closing the lid. So, it won't wake up again or rather, it isn't asleep (blinking lights indicate the difference). When booting again, I can choose to start up in recovery mode ... I checked all packages and the file system, updated the boot-loader (2.04-1ubuntu26.6), etc. In some cases, the system won't start up at all. I couldn't find a pattern yet.

I found this post describing that the screen remains black after waking up, but adding the option GRUB_CMDLINE_LINUX="nouveau.modeset=0" to grub (/etc/default/grub) didn't help.

I am out of ideas. Some further info:

$ ls -al /var/crash
total 8
drwxrwsrwt  2 root whoopsie 4096 Feb  9  2020 .
drwxr-xr-x 16 root root     4096 Nov 14 11:04 ..

and

$ls -al /usr/share/gnome-shell/extensions
total 20
drwxr-xr-x 5 root root 4096 Nov  5 22:00 .
drwxr-xr-x 7 root root 4096 Nov  5 22:11 ..
drwxr-xr-x 2 root root 4096 Nov  5 22:00 desktop-icons@csoriano
drwxr-xr-x 3 root root 4096 Nov  5 21:33 ubuntu-appindicators@ubuntu.com
drwxr-xr-x 3 root root 4096 Nov  5 21:34 ubuntu-dock@ubuntu.com

and the system (Asus notebook -- no Nvidia graphics)

$ lspci
00:00.0 Host bridge: Intel Corporation Xeon E3-1200 v5/E3-1500 v5/6th Gen Core Processor Host Bridge/DRAM Registers (rev 08)
00:02.0 VGA compatible controller: Intel Corporation Skylake GT2 [HD Graphics 520] (rev 07)
00:04.0 Signal processing controller: Intel Corporation Xeon E3-1200 v5/E3-1500 v5/6th Gen Core Processor Thermal Subsystem (rev 08)
00:14.0 USB controller: Intel Corporation Sunrise Point-LP USB 3.0 xHCI Controller (rev 21)
00:14.2 Signal processing controller: Intel Corporation Sunrise Point-LP Thermal subsystem (rev 21)
00:15.0 Signal processing controller: Intel Corporation Sunrise Point-LP Serial IO I2C Controller #0 (rev 21)
00:15.1 Signal processing controller: Intel Corporation Sunrise Point-LP Serial IO I2C Controller #1 (rev 21)
00:16.0 Communication controller: Intel Corporation Sunrise Point-LP CSME HECI #1 (rev 21)
00:17.0 SATA controller: Intel Corporation Sunrise Point-LP SATA Controller [AHCI mode] (rev 21)
00:1c.0 PCI bridge: Intel Corporation Sunrise Point-LP PCI Express Root Port #1 (rev f1)
00:1c.5 PCI bridge: Intel Corporation Sunrise Point-LP PCI Express Root Port #6 (rev f1)
00:1f.0 ISA bridge: Intel Corporation Sunrise Point-LP LPC Controller (rev 21)
00:1f.2 Memory controller: Intel Corporation Sunrise Point-LP PMC (rev 21)
00:1f.3 Audio device: Intel Corporation Sunrise Point-LP HD Audio (rev 21)
00:1f.4 SMBus: Intel Corporation Sunrise Point-LP SMBus (rev 21)
02:00.0 Network controller: Intel Corporation Wireless 7265 (rev 59)

Since there are usually not two separate root causes, I suspect that both errors are linked. Thx

Update I reconfigured my swap partition (see those two very informative posts on a step-by-step-guide here and for encrypted swap here). Nevertheless, I still experience the problem. Further, after crashing at suspend, the system starts-up automatically. However, when choosing "ubuntu" from the recovery booting list, the screen remains black and no startup is visible.