I'm currently trying to post on serverfault. When I try to search for a tag, the dropdown is empty. I have verified in Chrome debug tools that the call is being made and results are being returned as expected. I have no console errors. I have disabled all ad blockers and any CSS modifying extensions.
I reproduced the behavior on Stack Overflow and even here, on this post. The only reason I was able to select BUG is because meta seems to have additional behavior of showing a few tags as soon as you click. But once I start typing I get the same results as seen in this gif: