i have successfully done the same in my kindle but with the system 7.4.6, i think is the system.
what i have to do? i dont have any idea, this never happened to me
edit: installed the backup i made with twrp and booted. i m going to downgrade version. i think is the best method
edit: i need 7.4.6 .img because everytime i download the update (7.4.6) the kindle updates to 7.4.8 !