When I was writing the geography section of Home Creek, Queensland, I needed to add a number of links to other articles. Which means a number of times the "Add a Link" pop-up appeared. Each time, the pop-up didn't just appear but sort-of bounced into view appearing and then re-appeared slightly higher on the screen (the underlying edit window is scrolling up at the same time, but that's normal).
Now there are two scenarios with using Add a Link, one is that one of the link suggestions is the one you want. → split off to T231376
In the second scenario, the link I want wasn't one of the suggested ones, so I go to the search box in the pop-up to start typing the name of the article I want (I know what it is). On typing the first character, the Add a Link box jerks upwards so its top is hard against the bottom of the VE too bar. Again, annoying but maybe it's trying to create more space below to display suggestions, I think. However as I type each character and it changes its list of suggestions, the Add a Link box is jerking down-and-up a couple of times and the background edit window and the usual Wikipedia left-hand tool bar is also jerking up and down too (but the VE toolbar stays still). This jerking continues until you have typed so much of the name of the desired article that the list of suggestions is small enough to display on screen. For example, if I try to link Patrick to Patrick, Queensland (which is not one of the default suggestions), I have to type every letter of Patrick, Queensland and my screen is jerking about with every letter. I wish I could video it.
This is something that has changed in the past 24 hours. I was writing similar articles yesterday and not observe all this screen jerking going on.