Comment 4 for bug 1730331

Here is another confirmation of this bug:

https://bugzilla.redhat.com/show_bug.cgi?id=1490172

and downgrading to a previous version of linux-firmware (as suggested above, and to xenial-updates in my case), made the problem disappear:

$ dpkg -l | grep linux-firmware
ii linux-firmware 1.157.13 all Firmware for Linux kernel drivers