I can see that there’s a lot going on it this demo. There are two tables switched by arrow buttons and the window is getting bigger with a click inside of the table.
You would want the window to stay the same in size regardless the size of the table?
However this would fixed my problem (not completely), when I click autocomplete cell and dropdown menu appear, the vertical scroll bar is mysteriously appeared and disappeared. https://jsfiddle.net/4zwe90un/13/