How does the blocks execute

I now have tested this isue. But no matter what I do the time to clone 50 empty button in af row takes almost 1 minute inside my ap. I du this as the first thing when the screen opens.
If I make a new app with the same block to copyin a row it works fine and is very fast.
What can slow this function so mutch in my app The strange is that it is the first thing I do…
On the picture i start repeating the clone block as the first thing. But it takes almost a minute to clone.
It work the same way without the timer…