Doorbell Pro stops working after install of 2nd Doorbell Pro

I've had a Ring Video Doorbell Pro for a few years. I just aquired a 2nd Ring Video Doorbell Pro. Three days after installing my 2nd Doorbell Pro, the original one stopped working. Each one has the battery pack installed on the doorbell transformer - the original connected to "front;" the new one connected to "rear." Both have a lead connected to "trans." Is there some sort of incompatibility between the battery packs or the doorbell that is causing the original one problems??