Links between German and English pages disappear

Dear Community, we are using the Polylang plugin for several years now. I have a page with two languages, German and English. Most of our pages and content is available in both languages.

For two recently (within the last two weeks) created sub-pages I face the following issue: I created the German page, created the English version of it via clicking the “+” in the overview of all pages to have it linked automatically to the correct German page. I finalized the content and published the pages. When I tried the language switcher, the link between German and English is gone (I get directed to the homepage of the respective other language) – and when I look into the overview list of all pages, the pencil sign is also gone and the “+” is shown again as if no translation of the respective pages would exist.

1. German page: Success Story BMW DVS – Prozesse & IT-Systeme | EDLER & STIEGLER (edlerstiegler.com)
2. and English translation: Success Story BMW DVS – Processes & IT Systems | EDLER & STIEGLER (edlerstiegler.com)
3. German page: Success Story tegut… – Einführung Kassensystem | EDLER & STIEGLER (edlerstiegler.com)
4. and English translation: Success Story tegut… – Introduction POS system | EDLER & STIEGLER (edlerstiegler.com)

Strange thing is: it all works perfectly fine for other pages I created in the same time period? E.g. Success Story Endpoint Protection und Compliance | EDLER & STIEGLER (edlerstiegler.com)

We have:
1. Polylang version 3.5.3
2. wordpress version 6.4.3
3. php version 8.1.24
4. Current theme: the7 v.11.11.0

To solve the issue, I updated all themes plugins etc., I created the pages again completely from scratch, did not help.

Any suggestion for resolving the topic would be highly appreciated.

Thanks in advance!

The page I need help with: [log in to see the link]