If you work on more than one device, it may be possible that sync conflicts occur. Usually, iCloud sync is very stable, and you should not lose any data. Nevertheless, the app will create a backup of your songs before syncing with data from iCloud if there are fewer songs present in your iCloud than on your device.
You can restore them by accessing a hidden feature.
Navigate to "General information" in the sidebar menu. Scroll all the way down to the bottom, then tap five times on the app version.
If there is a backup present, in the following dialogue, there will be an entry looking like "Restore 12 songs from 08/02/20"