I think they stopped using the Yandex index at some point and solely used Bing's index. This may have been the cause.

I tried kagi some time ago, and I liked it a lot for similar reasons as the author. It has everything which made DuckDuckGo such a joy to use, ánd reliably good sesrch results. I also love the filter site and boost options, and the fact that the most used are shared on a "leaderboard".

The part I didn't love was the (understable, but annoying) need to login. This is especially a pain when you use a lot of different devices, delete cookies and friends regularly or use private browser windows. I tried using the method where you need to supply the ligin token manually, but, if I recall correctly, it was a painful experience because once you logged in elsewhere it would change, so it became an effort to keep the token in sync manually on all devices.