Possible errors after permalinks modifications

My current WP configuration
? PHP / MySQL version: less than 5.6
? Theme used: Viewport
? Extensions: Askimet, AMP, Google Adsense, GADWP, Image Widget, Polylang, Publish to Apple News, Redirection, Simple Light Box, WP Rocket, Yoast
? Name of the host: Infomaniak
? Website address: yesicannes.com and yesicannes.com/fr

Hi there,

Two changes in permalinks resulted in a chaos in the URLs, causing countless errors 404. Someone from WP.org support suggested the 404’s could come from URLs rewriting by Polylang. Would someone please be so kind as to take some of his precious time to see if my issue has something to do with Polylang?

YesICannes is a web magazine in 2 languages: yesicannes.com and yesicannes.com/fr. Our articles are indexed in GoogleNews, so the articles’ URLs must include some numbers.

Until recently, my permalinks were: yesicannes.com/%postname%
To add the numbers desired by Google, I used to preview the post and then manually added the generated “post id”, separated from the title of the article by a “-“.

Then, I thought to do this insertion automatically by modifying the permalinks with the following form: yesicannes.com/%postname%/%post_id%/.
Surprisingly, the links were displaying: yesicannes.com/postname/post_id/post_id/ with twice the number automatically inserted (!?)
But I did not have an alert from Google.

But I thought that with a “/” as a separator, it did not look like the URLs created so far, and I changed the permalinks a second time from “/” to “-” to get yesicannes.com/postname%-% post_id%/

I then started receiving calls from visitors who had 404 errors in the latest published reports and Goolge sent me a mail talking about augmented 404 errors on https://yesicannes.com/ and https://yesicannes.com/fr/, (type message [WNC-658800]).

Well, I understand that going from “/” to “_” can create 404 errors, and I realize my mistake. But the problem is more disturbing: the 404 errors display this kind of link, i.e. whereas the normal URL is: https://yesicannes.com/fr/mouratoglou-tennis-academy-sophia-antipolis-33009), the bad link is:

https://yesicannes.com/fr/mouratoglou-tennis-academy-sophia-antipolis-33009/33009/mouratoglou-tennis-academy-inauguration-10/

Another example of error 404: (whereas https://yesicannes.com/fr/mouans-sartoux-miel-ciel-provence-36831/ is good)

https://yesicannes.com/fr/mouans-sartoux-miel-ciel-provence-36831/36831/fete-du-miel-mouans-sartoux-2017-12/

The number is repeated with some kind of replication of the name of the post… Would anyone have an idea id Polylang URl rewriting has to do with this embarrassing situation?

Thank you in advance for your help.

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