Sorry that you're getting an error while syncing images from Lightroom. It seems like an issue with the sync location.
Change the destination of the folder that is currently syncing to your mobile photos. Try going into Lightroom Preferences > Lightroom Sync > uncheck the box that Specifies the location for Lightroom CC ecosystem's images or change the location to your SSD temporarily. You can change it back anytime or not use it at all.