Indeed, that looks unusual. I did find one old report on the debian- user list that's similar, but was ultimately unsolved[0].
If you're getting two duplicate emails, that indicates logcheck is running from both the crontab and new systemd timer. In that case, can you share the contents of /etc/cron.d/logcheck? If you had locally modified that file, it might not have been properly updated to not run in a systemd environment. Richard provided several good things to check that will help track down the root cause of this issue. Mathias [0] -- https://lists.debian.org/debian-user/2023/06/msg00163.html
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