I had a problem recently on a website using WordPress and the Enfold theme. A YouTube video that was initially marked as private, but later updated to public (embeddable) was still only showing the link, and not the actual video player.
Other videos however in the same page, where showing properly.
It turns out that from reading here that WordPress does some caching and is not pulling the latest youtube change.
To fix the problem, connect to the MySQL client, and retrieve all pages with an embedded video:
mysql> SELECT * FROM wp_postmeta WHERE meta_key like '%_oembed%';
My results were something like this:
+---------+---------+-----------------------------+------------------------------------------+
| meta_id | post_id | meta_key | meta_value |
+---------+---------+-----------------------------+------------------------------------------+
| 306 | 86 | _oembed_5c3aff6d73f219 | {{unknown}} |
| 336 | 10 | _oembed_39378045d82af3 | {{unknown}} |
| 337 | 10 | _oembed_a26684b605680e | {{unknown}} |
| 354 | 86 | _oembed_af60fe80d2fe16 | <iframe src="yt.com/S3edckDk_qo></iframe>|
| 355 | 86 | _oembed_time_af60fe80d2fe16 | 1503662521 |
| 356 | 10 | _oembed_f4d0e4e5251dea | <iframe src="yt.com/S3edckDk_qo</iframe> |
| 357 | 10 | _oembed_time_f4d0e4e5251dea | 1503662579 |
| 359 | 71 | _oembed_time_a26684b605680e | 1503662615 |
| 385 | 138 | _oembed_f4d0e4e5251dea | <iframe src="yt.com/S3edckDk_qo</iframe> |
| 386 | 138 | _oembed_time_f4d0e4e5251dea | 1503777685 |
| 387 | 138 | _oembed_4c76e997d8b21a | {{unknown}} |
| 389 | 138 | _oembed_268d95c8d907aa | {{unknown}} |
| 391 | 138 | _oembed_time_a26684b605680e | 1505355944 |
+---------+---------+-----------------------------------------------+------------------------+
I tried removing the offending meta_id, by issuing:
mysql> DELETE from wp_postmeta WHERE meta_key like '%_oembed%' and meta_value like '%OeiZNr24o7g%';
However that didn’t work when I refreshed the page, so I decided on the more radical solution:
mysql> DELETE from wp_postmeta WHERE meta_key like '%_oembed%';
That solved all my problems!