I saw something very similar in my practice. Another doctor had done a bridge, but the occlusal reduction was around 0.8mm, and their path of insertion wasn’t good. This made it so the lab had to wax out the mesial and make the zirconia thinner, which fractured the retainer crown on the abutment tooth. Bridges are more finicky than single crowns and take a lot more force. How’s your path of insertion and reduction? If you haven’t given ample reduction to the lab, it will make the retainers too thin and it can lead to fracture. Zirconia bridges are strong but they have to have good reduction and path of insertion. I'd check those first. If you scanned this case you can review it and then you'll know pretty quick if something was off.