workaround
I've just installed the 4.4.2 update on my Advent-branded Tegra Note and the first boot was painfully slow. The "Optimizing Apps" stage of the boot took more than an hour for 161 apps and when the boot was complete the device was lagging to a ridiculous degree. Swiping left or right on the home screen resulted in a jittery page change after maybe 6 or 7 seconds. I eventually had to force a shutdown. Subsequent boots have started OK but with periodic lag for 20-30 seconds at a time. Has anyone else had issues like this?
This is not a solution, but instead a workaround that seems to work.
a) Firstly you need to turn on the 'developers options' in the settings menu.
Go into 'Settings' > 'About tablet' then tap the 'Build number' seven times.
You will get a message telling you that you are now a developer.
Return to the main settings page and a new option 'Developers options' will be visible.
B)Click on 'Developers options' > 'Select runtime'. Then click 'Art'. This cause android to rebuild the runtime system & libraries. When its finished optimising apps, use the tablet as normal for 10-15 minutes, note some apps will NOT function properly.
Restart tablet by powering off and turning back on.
C)Goto main 'Settings' page click 'Developers options' > 'Select runtime'. Then click 'Dalvik'. Android will rebuild the runtime system & libraries and return the tablet to its original state. When its finished optimising the apps, Power off the tablet then restart.
I hope this helps… (does not require unlocking or rooting)