Unhappy [Q] Soft Navigation Keys Disappear on 8.4.6

I have a Kindle Fire HD 8.4.6, rooted with Hashcodes 2nd Bootloader guide and TWRP and Seokhun's excellent instructions. I am having a problem with the soft navigation keys consistently disappearing upon booting up. I have since restored my origional backup files, but retain the 8.1.4 bootloader and SuperSU.

Can someone help me retain the disappearing navigational keys?