This issue has already been raised with zero response/support here: https://community.spotify.com/t5/Android/Spotify-connect-problems-need-to-reinstall-to-fix-it-each-t...
Have tried to get this working countless times on a Pixel 2XL and Pixel 3 with fully updated versions of Spotify. Have made sure echo devices are fully updated, freshly restarted, and I re-linked the spotify account to the Alexa app. The post linked here describes my exact issue. Spotify Connect will only list "devices available" for Echo devices on a fresh install. Nothing else works. Went to work, and came home, and sure enough, Connect is completely unresponsive. Considering just dumping my Premium account because this has been an ongoing issue for months.