[wp-trac] [WordPress Trac] #33148: Categories are missing in admin category list when child category linked to non-existant parent id

[WordPress Trac]

#33148: Categories are missing in admin category list when child category linked to
non-existant parent id
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 Reporter:  ShawnLunny               |       Owner:  (none)
     Type:  enhancement              |      Status:  new
 Priority:  normal                   |   Milestone:  Future Release
Component:  Taxonomy                 |     Version:  4.2.3
 Severity:  normal                   |  Resolution:
 Keywords:  needs-patch ux-feedback  |     Focuses:  administration
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Comment (by siteadvice):

 I think it's worth pointing out that this problem occurs on the front end
 of the site, not just the Dashboard. As you might expect, the list of
 categories is only partial, no matter where you're calling it from.
 In my case, I think I may have isolated the source of this issue.
 Someone deleted the category "Uncategorized" (not sure if this was done
 via the dashboard, using a plugin or possibly via phpMyAdmin - I don't
 have any log of it) but they did not set a new default category in
 Settings > Writing. Setting a new default category seems to have fixed the
 problem, but it's hard to be 100% certain because the issue arises
 occasionally and I haven't been able to identify what triggers the results
 set to stop working properly.

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Ticket URL: <https://core.trac.wordpress.org/ticket/33148#comment:16>
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