Comment 9 for bug 1907432

Quick note on a workaround: I've found on my pi400 that reverting to kernel 1007 works around the issue. If you've still got 1007 installed (a quick "ls /boot" should confirm that if you see lots of *-1007-raspi files lying around) you can temporarily switch to it like so:

$ sudo flash-kernel --force 5.8.0-1007-raspi

This will force flash-kernel to copy the older kernel (and dtbs etc.) to the boot partition instead of the latest (obviously you need to reboot afterward to use the 1007 kernel). flash-kernel will warn in its output that installing another kernel will just overwrite this, but that's *probably* what you want anyway (assuming the next upgrade fixes this).