Unfortunately those two ADB commands plus rebooting the tablet did change: nothing :-(
I used Fire Toolbox to
- hide few Amazon apps using "Manage Amazon Apps" (Simple mode)
- try to remove Device Dashboard button in navigation bar (bottom) (which didn´t work and resulted in 3 main action buttons been spread way to far on the screen so I had to ADB command "settings put secure sysui_nav_bar "space,space,space,back;home;recent,space,space,space"" which was recommended in this topic too) - that was before the FireOS update and everything was working fine at that point
- remove/reposition items in control center menu (top menu)
- try some screen capturing
- try to create a system backup
So indeed those things broken now have been touched using Fire Toolbox.
Another two small pieces of information:
a) for a few days I have the download manager complaining about a "failed download" for Google Play. Important: I installed Google Play manually a long time ago and did not use Fire Toolbox for that.
b) Freshly after reboot I get a popup (enabled those in developer tools) that "DavsClientService" has been stopped. Not sure if that is related in any way, don´t think so.
Hope all that information helps you to help us! I really do. :-( :-( :-(