Why I can not work with MIT App Inventor on low-end tablets?

Since when is it not working?
This is the last uploaded aia file by you:

Difference in output of text length depending on from where it comes, list direkt, or list with blocks between - #83 by Gunnar_Scott_Freiher

How much work did you do since that?
Last resort you can login with the autoload=false option that @Patryk_F gave you and export your aia file, post here and somebody try to take a look on it.