Thanks, @maheshmaharjan
Now, when I try your suggestion as-is on the main page, the LOAD MORE link appears broken – on top and behind the grid content.
I also tried the setting without Item Selector (I left it empty).
Then the LOAD MORE link appears correctly below the 4×4 grid and it works, but when more posts are loaded the grid breaks: it is no longer 4×4, rather than the first and the last newly loaded rows display only 2 posts. Only the 2nd and 3rd newly loaded rows are displayed correctly (4×4 grid).
I am resetting the plugin to default for now, in order to disappear we find a way to fix it. Any clues? Thanks for your efforts ??