[Users] Some msgs have (No Date) for the date

[mnieuw at zap.a2000.nl]

From one origin only, messages have started to appear with (No Date) as
Date in the inbox view. This happens with almost all messages, but not
all. Both on versions 3.17.8 and 4.0.0 , on Linux.

Looking at the headers (Ctrl-H), there are 5 "Received:" entries, each
has at the end a semicolon followed by a date. The dates are of the
format "Mon, 16 Aug 2021 22:10:28 +0200 (CEST)" The (CEST) is missing
on some fields, the +0200 can be +0000 (UTC) too.

How can I find out where to look for a change?

Mat Nieuwenhoven