So I created a Safari Web Extension. I did not change any piece of code and ran the template code provided by Xcode. I clicked on the toolbar item and a blank popover window popped up. It took around a good 5 seconds to load the "Hello World!" screen (It is the screen that is the part of the template Xcode provides). After that, whenever I again clicked on the toolbar item, the "Hello World!" screen popped up immediately, but Safari did not respond until around another 5 seconds.
Is this a bug on Apple's part or am I missing something? I am using Xcode 12.2 and Safari 14.0.1
Note: This does not happen on a Safari App Extension
It's a bug in Safari right now. I've had it reported with Apple for quite a while under FB8976225. But the great news is it looks to be resolved in Safari Technology Preview Release 124. I'm hoping we will see it moved to the Stable channels soon.