By default, the base style of GridItem component is:

export const gridItemStyle = tva({
  base: `w-full`,
});

And in the grid/index.tsx, line 322 -> 338, GridItem component:

return (
  <View
    ref={ref}
    // @ts-expect-error
    gridItemClass={gridItemClass}
    className={gridItemStyle({
      class: className,
    })}
    {...props}
    style={[
      {
        flexBasis: flexBasisValue as any,
      },
      props.style,
    ]}
  />
);

The result is that the column spanning of the items are not following the class names (which is then calculated for the flex basis), but the w-full instead. I tried changing flexBasis to width, and it just worked properly.