PDF repeating the beginning and the end of some lines of text

Hello, does anyone knows what causes the PDF to repeat the beginning and the end of some lines of text?

For example, my text is: "I would like to write you a letter", visually it looks like that, but if I try to copy it, it pastes: "I would like to write you a letterI letter". It's not just copying, trying to select the text in the PDF also shows the word duplication to the point that it prevents me from selecting the first and second line correctly, because it keeps selecting a phantom "I".

I checked using "Edit PDF" if there was any funny bussiness with the text, but it shows a single textbox with no repetition nor any weird text bellow it. The Indesign original also has no duplication and look very standart. I tried to open it on different computers, the error occour on all, on the same lines. I also checked the PDF export configurations, it is the same as we always use, pretty close to standart.

Just in case it is relevant, the documents are in Portuguese, but the error occurs even in lines without special Portuguese characters. The error also occurs on different lines within the textbox, sometimes in all of them, sometimes not, sometimes in the first line, sometimes just in the middle, some textboxes have no issues -- it's pretty random.

I appreciate any help, this is quite maddening.