Permalinks are mixed-up between languages suddenly

I am the owner of the website stuartmcmillen.com, which offers content in multiple languages using Polylang Free. English is my main language, and the others are translations.

In the last 24 hours, I have had multiple English langauge users contact me to say that many of my URLs are now pointing to translations in other languages.

For example, when users try and visit the English language Supernormal Stimuli at its normal address: https://www.stuartmcmillen.com/comic/supernormal-stimuli/ …
…they are instead being redirected to the Italian language comic: https://www.stuartmcmillen.com/it/comic/supernormal-stimuli/

Ditto when people try to read my English language Rat Park comic at its normal address: https://www.stuartmcmillen.com/comic/rat-park/ …
…they are instead being redirected to the Russian language comic: https://www.stuartmcmillen.com/ru/comic/rat-park/

Also: https://www.stuartmcmillen.com/comic/war-on-drugs/
https://www.stuartmcmillen.com/de/comic/war-on-drugs/

and
https://www.stuartmcmillen.com/comic/thin-air/https://www.stuartmcmillen.com/zh/comic/thin-air/
https://www.stuartmcmillen.com/comic/type-iii/https://www.stuartmcmillen.com/zh/comic/type-iii/

Looking into the backend of WordPress, it seems that some of the English posts have had their slugs renamed to things like /supernormal-stimuli-2/

As you can see, these are all posts where I originally had the URL slug as exactly the same as the English version.

When looking at the documentation for Polylang, I see that Polylang now only supports slugs in multiple languages for users who pay for Polylang Pro. This is something that I wasn’t aware of until now.

Just wondering if this is a new feature that may now be impacting on my website?

Looking at archive.org snapshots of my website, I can see that until now, I have been supporting translations that have featured the exact same slug as my English language content. e.g. the Russian version of Rat Park, with /rat-park/ as the slug (same as the English slug), and the Russian War on Drugs with /war-on-drugs/ as the slug.

Is it possible that previous my Polylang Free was supporting identical slugs, and something caused my WordPress installation to stop supporting identical slugs, and to change a lot of URLs.

Anyway, I’m disappointed that things have suddenly broken, and am hoping someone can let me know what has happened, and how to fix it.