Hi @tiagozt, I completely understand your situation. As a workaround, I think you should try Xodo docs (if you're using highlighting in Android). Xodo is more suitable for this purpose and every change you do in the file will be prompt to save by EN.
About this especific feature (Highlighting pdf files), I like to use Xodo because the app summarizes the highlights, allowing me to do a quick review of the content I deemed relevant.
Hope that helps!