Plus icon not showing for some pages

hello
i’m designing a multilanguage website (Italian-English).
I created a few weeks ago the Italian version of some pages (website main language is English). Then I deleted them because they were to be completely redesigned, so it was easier to design them from 0 than to modify. Now I’m going to create them again, because website version is definitive, but I cannot add them in the dashboard. the old pages are nowhere (not even in the bin) so I should be able to add them from zero, shouldn’t I? but under the language column in the dashboard, I cannot see the + icon for the pages I previously deleted (like About and Contact – see screenshot https://snipboard.io/ZIWFrY.jpg).

I tried to create a new page from zero, in order to assign it later to its English version, but inside the English page (in edit mode) I cannot write in the Italian field https://snipboard.io/bdeQzU.jpg, and inside the Italian page I cannot find the English version https://snipboard.io/HirN2R.jpg

Do you have any idea why so?
I tried to disable all plugins but nothing changed. Polylang works fine except for those pages I previously created and deleted. Now I cannot retrieve them, so can you pls help me out?

Thanks in advance for ypur help.

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