System freeze: fifo: SCHED_ERROR 0a [CTXSW_TIMEOUT]

I have been experiencing freezes on my Dell Precision Tower 3620 with NVidia GM107 graphics card and a large 3840 × 2160 screen for some years now, with both Ubuntu 18.04 and Ubuntu 20.04, possibly with Ubuntu 16.04 too - I cannot recall. It often happens while viewing video in vlc, but also during simpler tasks such as reading mails in Thunderbird.

Here are the contents of the /var/log/syslog at the time of the freeze;

Feb 26 11:18:15 xxxxxxxx kernel: [15385.625416] nouveau 0000:01:00.0: fifo: SCHED_ERROR 0a [CTXSW_TIMEOUT]
Feb 26 11:18:15 xxxxxxxx kernel: [15385.625436] nouveau 0000:01:00.0: fifo: runlist 0: scheduled for recovery
Feb 26 11:18:15 xxxxxxxx kernel: [15385.625453] nouveau 0000:01:00.0: fifo: channel 6: killed
Feb 26 11:18:15 xxxxxxxx kernel: [15385.625462] nouveau 0000:01:00.0: fifo: engine 5: scheduled for recovery
Feb 26 11:18:15 xxxxxxxx kernel: [15385.625467] nouveau 0000:01:00.0: fifo: engine 0: scheduled for recovery
Feb 26 11:18:15 xxxxxxxx kernel: [15385.626095] nouveau 0000:01:00.0: Xorg[2366]: channel 6 killed!

Mouse cursor stops moving, keyboard stops responding, virtual terminals cannot switch. Music continues to play. Sometimes I'm still able to log into the machine using ssh, sometimes I cannot even log in.

By the way, I don't know if it's related, but I'm mentioning this here for the sake of completeness: sometimes the screen starts flickering, the only way to fix that is to kill Xorg.