I too have been noticing a deterioration in recent months. Things that generally worked smoothly before have random bugs now. For example, turning off shuffle and resuming a song will sometimes just stop playing Liked Songs after the song ends, shuffle will turn off/on seemingly at random, etc. Also there seem to be odd inconsistencies in the UX between mobile and desktop such as liking songs and seeing Smart Shuffle songs in playlists.

I've been generally very happy with the Spotify app for years and it's disappointing to see the quality slipping.