Bullseye - who and users return nothing

["Gareth Evans" <donotspam@fastmail.fm>]

Hello,

I've just noticed that: 

$ who

and

$ users

both return nothing, with or without sudo.

$ sudo strace who
<snip>
access("/var/run/utmpx", F_OK)          = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/var/run/utmp", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
access("/var/run/utmpx", F_OK)          = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/var/run/utmp", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
close(1)                                = 0
close(2)                                = 0
exit_group(0)                           = ?
+++ exited with 0 +++

I found these which look at least semi-relevant for other distros;  the redhat link seems to suggest a failure at or before login.

https://www.suse.com/support/kb/doc/?id=000017277
https://bugzilla.redhat.com/show_bug.cgi?id=1396065

- but nothing for Debian - so any advice on how to proceed would be appreciated.

Can anyone replicate this or suggest what may have happened?  I'm fairly sure I've used who since upgrading from Buster.

Would try creating the files but I'm not sure of Debian's ownership/permissions requirements.

$ cat /etc/debian_version
11.2

Thanks,
Gareth