Hey @spinus1, welcome to the Spotify Community!
Do you have more than 1 device available for offline use? If so, do you hear the same pitch if you try to play a song in the Offline Mode from that other device?
Also, let us know the Spotify version you're running.
Keep us posted.
Hey there you, Yeah, you! 😁 Welcome - we're glad you joined the Spotify Community! While you here, let's have a fun game…