See my experiences to 3.4:
https://www.mobileread.com/forums/sho...d.php?t=196495
KF8 is the only thing that is not working.
I don't believe webkit library and kernel updates have anything to do with KF8 support. The log says unrecognized format when I tried to open a KF8 mobi file. Hopefully other expert can help to resolve this.