In the last few days, all the servers have been upgraded to the latest code.
There were multiple improvements in the Mailman code and a few bugs that have been fixed: mailing list owners can remove and reattach threads in the archive now, Hyperkitty renders messages correctly, and some domains with an irregular DMARC record are not blocked by Mailman anymore.
If you experience glitches in the Postorius/Hyperkitty UI, please perform a hard refresh of the page in your browser.