Video Doorbell 3 power problem

I recently installed a Doorbell 3. I hardwired it to the existing system. I have a 24v transformer, which shows 21.8v at the Doorbell. And I have an existing Nutone Scovill mechanical chime, which is listed under compatible devices. I also added a Ring Chime. After connecting the wiring to the Doorbell 3, I get a reading of less than 2v at the contacts on the back, and the app tells me it’s not hardwired. Additionally, the plunger on the mechanical chime is retracted and the chime is buzzing. The firmware is updated and I’ve tried updating the settings in the app. I’ve tried disconnecting the mechanical chime, but that doesn’t change anything with the voltage at the Doorbell. Is there a solution to this problem, or do I need to replace the Video Doorbell 3?