Well, we still have problems with the latest 2.3.2-2020033112 firmware... I've uploaded 2 videos showing how what you write in a pdf gets deleted as soon as you turn the page (just a bit before turning the page, exactly). I've sent am email to Boyue's technical support with both links, I think it's better this than trying to explain with words.
https://youtu.be/w5sGke-KOvs
https://youtu.be/TXwy7aphpE0