When exporting to PDF from a file including text variables, it results in text in pdf that it is impossible to highlight correctly. and therefore - it is impossible to mark PDF comments on it. Screenshot and PDF files are attached.
It only happened with ARIAL font, and only in certain book files (that were created in previous ID version). I couldn't recreate the bug in another file.
When I removed the text variables the PDF was exported fine.
I also had another kind of conditional text I made in these files - it was a sentence written inside the 'Text After' field in Bullets & numbering tab in a Paragraph style, and would show on book only when typing something (I used space) using this paragraph style. This kind of conditional text had the same effect on PDF text, and when removed - PDF got exported fine.

Indesign 14.0.1 on OSX 10.14.2