Smalltalk UIs used to work with only one CPU thread. Any action from the user would freeze the whole UI while it was working, but the positive aspect of that is that it was very predictable and bug free. That's helpful since Smalltalk is OOP.

Since React is functional programming it works well with parallelization so there is room for experiments.

> Especially if it involves content jumping around.

I remember this from the beginning of Android, you'll search for something and click on it and the time it takes you to click the list of results changed and you clicked on something else. Happens with adds on some websites, maybe intentionally?

> And the most annoying antipattern is showing empty state UI during loading phase.

Some low quality software even show "There are no results for your search" when the search didn't even start or complete.