Update:
So the device still being jailbreaked, Kual menu didn't show up because I accidentally delete it.
I restore the file and everything is fine again. 
Hello,
So here is how my nightmare begins:
I did jailbreak my Kindle Paperwhite 3 (when I bought it, it’s firmware was 5.6.5 ). I also did the hotfix stuff, then I updated to 5.7.2 manually. Everything was fine, I installed Kual, KoReader (I have a lot of pdf to read, and the default pdf reader isn't very good), the device and programs operate very well.
Today, I was trying to install some other stuffs (Python, Mobile Kindlet Kit, LibrarianSync). LibrarianSync doesn’t show up in Kual menu, so I think restarting the device would help, when it boots up, Kual doesn’t show up either. I checked the firmware version which is currently 5.7.4.1. I think the device losts Jailbreak because I did some bad installing steps
Here’s what I’ve tried
_ I restart the device (until now, it’s about 6, 7 times..), Kual doesn’t show up…
_ I reinstall the hotfix. I place the bin file in the root directory, when I ejected my Kindle, this message appear:
“Update Error: An invalid update file has been loaded on your device. Please go to
www.amazon.com ….”
Sometime, the above message doesn’t appear, but I can’t update the device (the “Update Your Kindle” is grey out )
_ I tried to re-jailbreak, but it doesn’t work.
_ And I've never reset my device.
Maybe when I install other stuffs, I did some steps incorrectly, but how come my Kindle losts its jailbreak
. I’ve done some research, but now I don’t know what to do.
Do you have any solution
Thanks in advance.
Update:
So the device still being jailbreaked, Kual menu didn't show up because I accidentally delete it. I restore the file and everything is fine again.
Thank you very much .