Happens for me as well. I feel like it's when transitioning to and from WiFi/cellular. Usually closing the app and reopening establishes a connection with Spotify.
Google Pixel 2 XL
Spotify 126.96.36.1993, premium subscription
Sorry for the delay.
We're currently investigating this offline isssue on this thread. As soon as there's an update, we'll post it there.
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All the best.
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