Search sees a word in one document, not in another one, although it's there

OK, sorry, I'll repost the whole message then :

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Hello,

I've just realised that the search tool (Ctrl + F) could work differently inside 2 very similar, almost identical documents, based on same template. Just see :

Adobe Acrobat Reader DC finds the 29 out of 29 occurrences of the (french) word "redevance" in this January 2019 edition of a Gas and Electricity provider's tariffsheet.

https://www.essent.be/fr/download/tariffsheet/B2C/20190129

While it only finds 6 out of the 28 occurrences of the same word in this May 2019 edition of the same document.

https://www.essent.be/fr/download/tariffsheet/B2C/20190529

Were these 2 docs actually (but invisibly) made differently, which would explain why Search tool works differently with one compared to the other ?

Thanks for any help