I'm having the same issue on an upgraded 18.04 -> 20.04.
This is bugging me immensely.

Ready to help out in any way. I have also confirmed that if I disable apparmor it works. But that is not a solution.

Here is an strace showing what it's up to starting at the socket access.

$ VIRSH_DEBUG=0 strace virsh list
...
access("/var/run/libvirt/virtqemud-sock", F_OK) = -1 ENOENT (No such file or directory)
access("/var/run/libvirt/libvirt-sock", F_OK) = 0
socket(AF_UNIX, SOCK_STREAM, 0)         = 6
connect(6, {sa_family=AF_UNIX, sun_path="/var/run/libvirt/libvirt-sock"}, 110) = 0
getsockname(6, {sa_family=AF_UNIX}, [128->2]) = 0
futex(0x7f22454da060, FUTEX_WAKE_PRIVATE, 2147483647) = 0
fcntl(6, F_GETFD)                       = 0
fcntl(6, F_SETFD, FD_CLOEXEC)           = 0
fcntl(6, F_GETFL)                       = 0x2 (flags O_RDWR)
fcntl(6, F_SETFL, O_RDWR|O_NONBLOCK)    = 0
futex(0x7f22454da180, FUTEX_WAKE_PRIVATE, 2147483647) = 0
pipe2([7, 8], O_CLOEXEC)                = 0
write(5, "\0", 1)                       = 1
futex(0x7f22454d9320, FUTEX_WAKE_PRIVATE, 1) = 1
futex(0x7f22454da078, FUTEX_WAKE_PRIVATE, 2147483647) = 0
futex(0x7f22454da150, FUTEX_WAKE_PRIVATE, 2147483647) = 0
write(5, "\0", 1)                       = 1
futex(0x7f22454d9320, FUTEX_WAKE_PRIVATE, 1) = 1
rt_sigprocmask(SIG_BLOCK, [PIPE CHLD WINCH], [], 8) = 0
poll([{fd=6, events=POLLOUT}, {fd=7, events=POLLIN}], 2, -1) = 1 ([{fd=6, revents=POLLOUT}])
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
write(6, "\0\0\0\34 \0\200\206\0\0\0\1\0\0\0B\0\0\0\0\0\0\0\0\0\0\0\0", 28) = 28
rt_sigprocmask(SIG_BLOCK, [PIPE CHLD WINCH], [], 8) = 0
poll([{fd=6, events=POLLIN}, {fd=7, events=POLLIN}], 2, -1) = 1 ([{fd=6, revents=POLLIN|POLLHUP}])
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
read(6, "", 4)                          = 0
openat(AT_FDCWD, "/usr/share/locale/locale.alias", O_RDONLY|O_CLOEXEC) = 9
fstat(9, {st_mode=S_IFREG|0644, st_size=2996, ...}) = 0
read(9, "# Locale name alias data base.\n#"..., 4096) = 2996
read(9, "", 4096)                       = 0
close(9)                                = 0
openat(AT_FDCWD, "/usr/share/locale/en_US/LC_MESSAGES/libvirt.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale/en/LC_MESSAGES/libvirt.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale-langpack/en_US/LC_MESSAGES/libvirt.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale-langpack/en/LC_MESSAGES/libvirt.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale/en_US/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale/en/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale-langpack/en_US/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/share/locale-langpack/en/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/x86_64-linux-gnu/charset.alias", O_RDONLY) = -1 ENOENT (No such file or directory)
write(5, "\0", 1)                       = 1
futex(0x7f22454d9320, FUTEX_WAKE_PRIVATE, 1) = 1
futex(0x55589445f510, FUTEX_WAKE_PRIVATE, 1) = 1
close(6)                                = 0
close(8)                                = 0
close(7)                                = 0
write(2, "error: ", 7error: )                  = 7
write(2, "failed to connect to the hypervi"..., 36failed to connect to the hypervisor
) = 36
write(2, "error: ", 7error: )                  = 7
write(2, "End of file while reading data: "..., 51End of file while reading data: Input/output error
) = 51
write(1, "\n", 1
)                       = 1
write(5, "\0", 1)                       = 1
futex(0x7f22454d9320, FUTEX_WAKE_PRIVATE, 1) = 1
futex(0x7fff571d7ca0, FUTEX_WAKE_PRIVATE, 1) = 1
futex(0x7f2240d6b9d0, FUTEX_WAIT, 134641, NULL) = 0
exit_group(1)                           = ?
+++ exited with 1 +++