What happened to the mailing list archive?

For a few weeks now, there's a gap in the openwrt-adm archive between May 2018 and June 2020 (as well as a lot of messages gone in June 2020). There was a discussion about 20.xx release there, as well as some references to the archive earlier this year on this forum (I can't find them now).
There are also some weird things in the openwrt-devel archive for June 2020, as well as some missing messages there.
Is it gone forever or is it fixable?

See https://www.mail-archive.com/openwrt-devel@lists.openwrt.org/msg53332.html