You’re suffering from one small issue that I also came across, and that’s if you load the data too quickly after creating the grid none of the formatting (for example “fitColumns”) kicks in.
In your example you don’t see it because you wait for the “refresh data” button to be clicked before loading the data. I do see it because mine gets loaded on the show_form event.
The way I got around it in my early version was I fired an event (table_created) from the JS and caught it in the Anvil form. I then initialised my data from there.
Just a thought.