OnI have experienced the same issue whereby the music stops and starts when the s10+ goes into lock screen. However, it appears to be a Samsung issue as it also happens with YT music and any Google Music. Hope a patch update corrects this ASAP as the issue does not happen when I play music from the device SD card or internal memory.
Been having the same issue on my s10+. Also had an issue where the controls on my beats wireless earbuds stop working and have to unlock my device and go into the app for them to work again....so frustrating
i think I figured it out... If you swipe up to bring up your app drawer then in the search type in optimize. Optimize battery usage will show up. Click on that then choose it again... in the drop down select all apps. Then scroll down to spotify and disable battery optimization.