[jberanek]

Originally Posted by jhowell

Known issue due to a change by Amazon. Will be fixed (as much as possible) in the next calibre release.

https://github.com/kovidgoyal/calibr...d2fa13fc1ae29e

Thanks for pointing me in the right direction. What an astonishing move by Amazon - it does look at face value like a "nerfing" of book sideloading.

(Just noticed that the "Send to Kindle" app doesn't even support Epub uploads)