netavark 1.12.1-8 introduced a change from iptables to nftables to fix #1091318.
1.12.x has known upstream issues with not removing old nftables rules upon container stop/restart, resulting in duplicate rules and unreachable containers.
These issues have been fixed in 1.13.1.
1.12.1 should be either be reverted back to iptables or 1.13.1 released.

Refer https://github.com/containers/netavark/issues/1129

We believe that the bug you reported is fixed in the latest version of
netavark, which is due to be installed in the Debian FTP archive.

A summary of the changes between this version and the previous one is
attached.

Thank you for reporting the bug, which will now be closed.  If you
have further comments please address them to 1092742@bugs.debian.org,
and the maintainer will reopen the bug report if appropriate.

Debian distribution maintenance software
pp.
Reinhard Tartler <siretart@tauware.de> (supplier of updated netavark package)

(This message was generated automatically at their request; if you
believe that there is a problem with it please contact the archive
administrators by mailing ftpmaster@ftp-master.debian.org)
Format: 1.8
Date: Sat, 11 Jan 2025 11:17:31 -0500
Source: netavark
Architecture: source
Version: 1.12.1-9
Distribution: unstable
Urgency: medium
Maintainer: Reinhard Tartler <siretart@tauware.de>
Changed-By: Reinhard Tartler <siretart@tauware.de>
Closes: 1092742
Changes:
 netavark (1.12.1-9) unstable; urgency=medium
 .
   * Revert back to using uptables. Closes: #1092742, Reopens: #1091318
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 e883ce998dba87fad01cc884cbecbaa0 19636 net optional netavark_1.12.1-9.debian.tar.xz
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