Originally Posted by Hollow Man

Does amazon also delete azw3 files? I only know of it happening with kfx/azw8 since I experienced it.

There have been reports of azw3/KF8, KFX and mobi files being deleted. All that seems to be required is for the book to contain an ASIN matching an Amazon book that you don't own/have a loan of an Amazon copy and to keep your Kindle from connecting to Amazon for a long period.

In my testing, since I use the ISBN and ASIN for downloading metadata, my calibre generated Amazon format books had an ASIN. Since most of the books were sourced from Kobo, StandardEbooks, etc. in ePub format, I did not own an Amazon copy. When I took my Paperwhite 4 out of airplane mode after 5 or 6 weeks, most of the ebooks I had sideloaded vanished (according to the log files, they were deleted). Not a big deal to me since I only use the PW4 for testing ebooks I am formatting but for others where their Kindle is their prime ereader, an extremely annoying action. //

Yes, Amazon keeps track of which Amazon-sourced books are supposed to be present on each of your Kindle devices and will in some circumstances remove any unexpected copies. //

I see there is some theory that not having an ASIN may help with stuff not being deleted? Not my experience. Some of my sideloaded stuff was fanfic from archiveofourown and so of course, no asin or isbn, etc. and it was still deleted.

I haven't tried the personal doc type vs ebook, but will give that a try. But I think I also saw that I need to send to device from calibre as kfx instead of azw3 for that? Is that right?

I had been keeping my kindle with wifi off but at the end of Nov. I took advantage of the $0.99 for 3 months offer of KU and so of course, wifi came on. Then my previously sideloaded books disappeared...

Is there anything else that came up over the 51 pages of posts that I should know about?

I may just keep my oasis in airplane mode and bring my k4bnt back out for KU only. //

You cannot change the type from EBOK to PDOC if you convert to AZW3. So yes, you'd need either to convert to KFX, use Send to Kindle, or keep your Oasis always offline.