Frank Saunders, MS-MVP OE wrote:
The unread message count that you see before entering a group is
only an estimate based on the message IDs. It will be thrown off
by any unused IDs.

What I find happens is that messages aren't being downloaded, so the
unread count is correct but the messages don't appear. This has
happened two or three times before over the last few years, on
different news servers, so I'm inclined to think there's some long
term bug here.

Tools | Options | Read
Uncheck the option to download ### headers at a time. The operation
of this option is flaky.

OK thanks, I'll try that. I'd set it back to the default as I'd been in some
hulking great groups for headers, like this one.