Thank you for posting and welcome to the community, I'm sorry to hear about the issue you are having with your Sleepbuds.
When you have noticed only one earbud playing, are both of them appearing in the app as connected? Or is the right one, which isn't playing any sound, not showing as connected?
If they are both showing in the app, I would recommend checking the ear tip of the Sleepbud that is not playing, to ensure there is no blockage in the eartip. I would also recommend rebooting the device the app is installed on, in case it is a communication issue between the app and your Sleepbud.