Thank you for your report. I downloaded the file that you attached and tried it out on my K3. I opened it in reflow mode, default options. It doesn't crash on K3. I was able to go through all the pages and back. But, it takes 10s or so to render a page. Also, pressing Alt-Back does cause a crash (it should just close the file, and go back to FileChooser). It goes back to Kindle software, but doesn't refresh the screen. Alt-G fixes that, but the title bar is not updated anymore. To get it back, you need to start Librerator again, and exit normally.
So, no framework restart on K3. There's definitely some problem there, but it's highly unlikely to be fixed by me. Sorry. I neither have K4NT nor time. I also lack motivation
. The file you attached can comfortably be read manually setting bbox and using fit-to-content-width mode.
For improvements in Reflow mode, wait for koreader to add support for K4NT. Users of K2/KDX/K3 may have more luck with the newest version of KPV, because it uses newer libraries than Librerator-R2.