There are actually two bugs I encountered, of which the one in the title is critical.
Some of the papers with previously added handwritten annotations crash the whole app when I try to open them. Tried to delete them from the device and re-download, but it is not helping. It is very frustrating, since iOS app is my main reading tool, and is critical for my work.
Second bug being that some of the highlights are not synced with the web version.