Do you have any code at all in the Designer Script window? Are you using that feature? It's new for B4A Ver 1.90.
You can use the Designer Abstract and manually set your buttons, etc. width, height, etc. in the 'grid', the section where all the properties are -- or -- you can set the height, width, etc. inside the Designer Script window using code.
I recommend doing it in the Designer Script window using code. When you connect your emulator to it, you can press F5 and see immediate layout changes that you have made in code.
Remember, when using Designer Scripts window, only placement and positioning and size code works, it's not like coding in the main IDE section where you can use any B4A code.
There is a bug confirmed in Ver 1.90 Designer Scripts where at least one line of code must be in the All variants script top window, so you can put anything in there as long as there is at least one line. I put all my code in the bottom section, specific to that template/variant. I too have the same tablet template you do.