I’m having this issue now! In my case it happens when clicking the link edit button in the wysiwyg field (I’m using it in a custom block) from the side panel edit. The link edit dialogue box is prevented from popping up because it’s trying to align to the left of the wysiwyg input, but since it’s too wide it just flickers.
If you make a link that’s towards the right of the input, it loads the pop way in the middle of the screen. But if you try linking text along the left side of the input, it just flickers. It doesn’t do it in the main edit screen though.
I’m on WP 5.7, in Mac Chrome, ACF v. 5.9.5.
I do not have my scrollbars set to always show (although I love it, it’s very buggy imo).
