() Eric Abrahamsen <eric@ericabrahamsen.net>
() Mon, 15 Feb 2021 15:54:58 -0800

   It means that the Gnus agent has saved nov/header data in its
   .overview file that it was subsequently unable to make sense
   of. Each header line is supposed to start with an integer
   indicating the article number being read. In your case, the
   line seems to start with "an"? Or maybe it looks like "an" is
   part of a date format that Gnus is expecting?

   Anyhow, it would be useful to see the (full) offending line
   from the .overview file in the corresponding agent directory.

Yeah, that was the full line (starts with "an").  While waiting
for your response (thanks, btw!), i looked in gnus.info for
something along the lines of "regenerate overview", but IIUC the
instructions there are not suitable for ‘nntp’ (the backend for
this particular group).

Afterwards, i found the offending line and deleted it (along w/
a bunch of versioned ".overview.N.~" backup files) .  So far, so
good; no errors yet...

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