The extension only adds the track to the queue once when requested, it uses the official Spotify API endpoint for that. However it’s possible Spotify does not know how to go back to the previously played playlist once it’s added to the queue. I would suggest trying to add a track that’s not in your playlist manually to the queue and see if the same happens.
I see, thanks for confirming! Unfortunately, I’m not able to troubleshoot it further as I haven’t been able to reproduce it myself. Please create a new post in #extensions channel on our Discord server https://discord.gg/dXez8Zh. It will help if you can record your screen showing how you use the extension, including triggering the SR button and how it gets added to the queue. Thanks!