I get there while doing tcpdump capture on ssh IPv6 traffic and seen
"invalid" values in DSCP field (in respect to IANA defined values) with
a default sshd config on Debian 13. It seems identical in unstable.
I see a patch qualified as "temporary" in #923879 from 2019 that is
still applied on Debian 13, named revert-ipqos-defaults.patch.
Mentionning that to friends, one of them points me to recent changes
commited in openssh around this topic, that, I think will make debian
revert patch unappliable or introduce a change in behavior, pushing
default system DSCP values (CS0 I beleive) instead of non DSCP compilant
curent values.
https://marc.info/?l=openbsd-cvs&m=175396095604983&w=2
This patch is still applied, saying that there was a bug in iptables -m
tos in 2019. I never found a clue that is was reported nor considered
upstream. Debian bug #923880 still open and seems to be in a dead state.
Could you reconsider revert-ipqos-defaults.patch for testing+unstable ?
As mentionned in one the two BR, Fedora since 2019 choosen to not revert
IPQoS default values and I am not aware that there is problems with that
nowadays.