One of the most incredible examples of this I have experienced was the update to the Android 'Pocket Casts' app. It worked great, had useful functionality and was easy to use and navigate. I had a paid version I thought was great value

Then, out of the blue, they replaced it with a re-write. The new app was slow, missing most of the functionality in the previous app (not esoteric stuff, but things like play lists). The new UI was incomprehensible (even to me, a developer) and the had a massive number of serious bugs, like deleting your podcasts, missing episodes, never downloading episode and marking things you never listened to as played. Over the last year or so they have been continually fixing things so now it's almost as good as the application it replaced.