Comment # 2 on bug 1110456 from Thomas Blume

(In reply to Thorsten Kukuk from comment #1)
> simple test: "logger aaa"
> 
> On openSUSE Kubic (current Factory) we use the same setup as with SLES:
> journald and rsyslog. On openSUSE Kubic the string "aaa" is only visible in
> journalctl, not in /var/log/messages. As result, this log entry is gone
> after a reboot. Which is critical for us, as it does not allow us to debug
> problems.
> 
> On SLES15, "aaa" is visible in journalctl and /var/log/messages.

Hm, I'm not able to reproduce the issue on a recent Tumbleweed.
After installing rsyslog and rebooting I get:

-->
c592:~ # cat /etc/os-release 
NAME="openSUSE Tumbleweed"
# VERSION="20180917"
ID="opensuse-tumbleweed"
ID_LIKE="opensuse suse"
VERSION_ID="20180917"
PRETTY_NAME="openSUSE Tumbleweed"
c592:~ # logger tblume
c592:~ # logger aaa
c592:~ # tail /var/log/messages 
[...]
2018-10-08T14:03:10.525978+02:00 c592 root: tblume
2018-10-08T14:03:16.917398+02:00 c592 root: aaa
c592:~ # 
--<

Have you got a machine where I can log in to see the issue?