@zatka/jjansen
The following applies to iOS, Content Server, Library Format V2!
First of all, the saved views worked flawlessly.
I set up a test library with 215 books and a mix of epubs and PDFs and tried to download all the books at once.
After several attempts, there were inconsistencies (10-20 books were missing), and it was only on the fourth new setup that it strangely worked straight away and without any problems - I don't know why.
Lesson learnt: Download the formats separately in case of problems. In one attempt, it didn't download the PDFs at all because there were some duplicate formats and the respective epubs had already been saved. But as I already said, that was no problem at the last try.
Unfortunately, I don't know if this will help you.