Sorry to unearth such an old thread but it's been happening to me since updating to v6.6
The way it happens for me is if I use incognito mode and then try to search something with a non-incognito window after having closed the incognito window.
I also found a way I can fix it without deleting any data. ! When I open any webpage by typing its full domain name, let the browser load the page and then select and right click on any text and select "Search DuckDuckGo" (or whatever your default search engine is) the browser snaps out of it and everything is back to normal
69e6d3fb-2a98-420d-adab-f3ab1672039e-image.png
I can replicate both the trigger and the fix 100% of the times.