[wp-trac] [WordPress Trac] #49751: Old Featured Images (Thumbnails) Broken in 5.4

[WordPress Trac]

#49751: Old Featured Images (Thumbnails) Broken in 5.4
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 Reporter:  ispreview        |       Owner:  (none)
     Type:  defect (bug)     |      Status:  new
 Priority:  normal           |   Milestone:  5.4.1
Component:  Post Thumbnails  |     Version:  5.4
 Severity:  major            |  Resolution:
 Keywords:                   |     Focuses:
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Comment (by ispreview):

 Spent the afternoon looking deeper into this and found a possible cause.
 Older 'Featured images' from very old versions of NextGen/NextCellent
 Gallery and WP releases seem to have a different ID format.

 For example, when looking at one of my older posts under the "postmeta"
 table in MySQL (old NextGen Gallery system from 2012) I see that the
 "_thumbnail_id" field gives a record like "ngg-547", which correctly
 corresponds to the ID number of the image itself in the gallery.

 However, if I re-add the same 'Feature image' to that same old post via
 the current NextGen Gallery and WP5.4 release, then the _thumbnail_id
 changes to being entirely numeric and a number that is not the same as the
 original image ID - "21848".

 My guess is that WP or NextGen changed how they handled images at some
 point in the past and this has been exposed by the WP5.4 code change at
 the root of this. Preference would be to revert the WP5.4 change in wp-
 includes/post-thumbnail-template.php back to WP5.3 or find another
 solution, one which doesn't involve manually updating tens of thousands of
 articles :).

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Ticket URL: <https://core.trac.wordpress.org/ticket/49751#comment:11>
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