It's happening for me on Chrome Version 70.0.3538.110 (Official Build) (64-bit), for what it's worth. Seems like the Edit Window / Modal / Popup has some sort of resize mechanism to it or tied to it and it repeats shrinking the width of some container on a loop but there's nothing to tell that loop when to stop / what minimum width the loop / shrinking should end at.
It's quite hilarious actually because it starts squeezing everything to the left then it literally just poofs out of existence leaving just the "X" of the close button behind.