Verified bionic, focal, and hirsute (hwe kernel in focal) with steps in comment #1.
The kernel packages in -updates hit the issue. The kernel packages in -proposed don't hit it.
ubuntu@mfo-aufs-bionic:~/aufs$ uname -rv 4.15.0-163-generic #171-Ubuntu SMP Fri Nov 5 11:55:11 UTC 2021
ubuntu@mfo-aufs-focal:~$ uname -rv 5.4.0-91-generic #102-Ubuntu SMP Fri Nov 5 16:31:28 UTC 2021
ubuntu@mfo-aufs-focal:~/aufs$ uname -rv 5.11.0-41-generic #45~20.04.1-Ubuntu SMP Wed Nov 10 10:20:10 UTC 2021
Verified bionic, focal, and hirsute (hwe kernel in focal) with steps in comment #1.
The kernel packages in -updates hit the issue.
The kernel packages in -proposed don't hit it.
ubuntu@ mfo-aufs- bionic: ~/aufs$ uname -rv
4.15.0-163-generic #171-Ubuntu SMP Fri Nov 5 11:55:11 UTC 2021
ubuntu@ mfo-aufs- focal:~ $ uname -rv
5.4.0-91-generic #102-Ubuntu SMP Fri Nov 5 16:31:28 UTC 2021
ubuntu@ mfo-aufs- focal:~ /aufs$ uname -rv
5.11.0-41-generic #45~20.04.1-Ubuntu SMP Wed Nov 10 10:20:10 UTC 2021