The _error field was newly introduced as part of T275268: Address "image" table capacity problems by storing pdf/djvu text outside file metadata.

I don't remember how metadata errors were rendered previously, though. If previously it simply said there was no metadata, then this might be considered an improvement as it at least surfaces the issue. Although it'd be better if it did so through a localised message rendered instead of the table.

In T286400#7203262, @Krinkle wrote:

The _error field was newly introduced as part of T275268: Address "image" table capacity problems by storing pdf/djvu text outside file metadata.

I don't remember how metadata errors were rendered previously, though. If previously it simply said there was no metadata, then this might be considered an improvement as it at least surfaces the issue. Although it'd be better if it did so through a localised message rendered instead of the table.

How about a hidden maintenance category? I've changed the title btw as Bald mountain.jpg is actually not on Commons (it's on enwiki), but I assume this could happen on any wiki.

It doesn't seem to be major issue (in a sense that it would block further roll out img_metadata refactor) but if you need me to work on it, I can spend some time on it once the big parts are out of the way.

In T286400#7204255, @Ladsgroup wrote:

It doesn't seem to be major issue (in a sense that it would block further roll out img_metadata refactor) but if you need me to work on it, I can spend some time on it once the big parts are out of the way.

That would be nice. I personally think a hidden maintenance category would be the most helpful so files with bad metadata can be searched/filtered for by those who might be interested in fixing it. The table could be omitted in that case as your average end user doesn't need to bothered/confused by possibly corrupt metadata.

The problem with trying to "fix" bad metadata is that the only fix is usually removing it. A maintenance category would quickly become unusable.

In T286400#7205735, @AntiCompositeNumber wrote:

The problem with trying to "fix" bad metadata is that the only fix is usually removing it. A maintenance category would quickly become unusable.

It might be usable if one wants to search for files with bad metadata by a particular uploader (provided the files are also categorized in an uploader category) or from a particular source that has some fixable issue. It can also indicate some upload error, in the example of Bald mountain.jpg the uploader probably uploaded the 1024px thumbnail from Flickr. Uploading the original may fix the issue, though in this particular case that's not an option because no source link was provided and the license seems dubious. But otherwise that would be an option.

If those are bad excuses, no error should be shown either. If it can't be fixed there's no point in making end users worry about it.

At any rate it would absolutely be no worse than https://en.wikipedia.org/wiki/Category:Files_with_no_machine-readable_description with 148,361 files.

https://en.wikipedia.org/wiki/File:Villa_Augusta_-_La_Tercia.jpg
https://en.wikipedia.org/wiki/File:Challenge.jpg
https://en.wikipedia.org/wiki/File:Links.jpg
https://en.wikipedia.org/wiki/File:Majors_Apartments_-_La_Tercia.jpg
https://en.wikipedia.org/wiki/File:Stgeorge.jpg
https://en.wikipedia.org/wiki/File:Swing00111.jpg
https://en.wikipedia.org/wiki/File:Amrum.grass.jpg
https://en.wikipedia.org/wiki/File:Amrum.beach2.jpg