After the plasmoid is expanded, only then the seekbar starts counting the length of the song. This issue occurs with spotify but doesn't with vlc and mpv(with mpris plugin).
Can you please explain in more details?
I am facing the same issue. When playing a song in Spotify the progress bar in the media widget is displaying incorrect progress. Here is the Screenshot: https://i.imgur.com/N5l2sR1.png You can see the progress from Spotify and the media widget is not in sync. I am on Kubuntu 18.10 with KDE 5.14.2
The bug is still present in plasmashell 5.17.5 on Manjaro KDE 18.1.5
Spotify's MPRIS implementation does not properly support seeking/positioning. This is a bug on their side.