I usually download ebooks from Anna’s Archive and transfer it to my Kindle through the service. But 1/10 times it fails, with no apparent reason. The particular ebook in question is https://annas-archive.org/md5/e310a253a9d85992129cc2b8dd351556. What’s the way out?
You don’t have to convert to mobi anymore. The Kindle backend supports epub for a couple of months already. I’ve also read reports that Kindle’s can now convert ePub by themselves if you copy ePub files via cable but I haven’t verified that myself.