I found a few instances of this problem in the community, almost two years old, but Spotify do not listen, do not read. Spotify pretends to make improvements, but they do not seem to.
When I switch off Last.fm, the app deletes password, switches last.fm back on and it pops up this error in the notifications. There is no way to get rid of this.
It should have been fixed within a few weeks, not within two years.