Recently my gnus started displaying (in the *Group* buffer) some groups
(which had previously no unread articles) with an unread "ghost" article
but which groups could not be normally entered.

Here is a description of what I observed:

1. When pressing <Return>, the cursor simply moves on to the next group
   line. The number of unread articles remains unchanged and non-zero.
2. When pressing <c> for `gnus-group-catchup-current', the unread
   article number becomes zero and upon <Return>, all read articles are
   displayed in the group. Upon exit from the group, upon "g"
   gnus-refresh the "ghost" unread article reappears.

Luckily, this being nnimap the situation can be recovered by removing
the .newsrc files and restarting gnus from scratch. This is not optimal,
as all other relevant configurations will be lost, such as group levels,
etc.

This issue has happened before, it is not the first time.

Attached are samples of 4 problematic groups in the newsrc.eld-problem file.
For example the "Bitcoin" group, the problem shows as.,
    - Total num articles: 42
    - unexist: 43
    - active: (active 1 . 43)

Similar with others.
The "Rent" group exhibits 4 "ghost" articles, the other groups 1.

It would be interesting to know:
  1. how such a thing can happen ?
  2. how can the situation be recovered without throwing all info out ?

Hopefully, this may contribute to making .newsrc and gnus more robust.