Smart lock connectivity

Here are a few potential causes and solutions:

• Security System Configuration: It’s possible that the security system is not properly configured to handle calls to mobile phones. You might want to check with the building management or the security system provider to ensure all settings are correct.
• Network Compatibility: Weak cellular signal (1-bar) might be affecting the quality of the buzzer calls. Since your iPhone is brand new and works fine otherwise, consider using Wi-Fi calling if it's not already enabled. This can sometimes improve call quality in areas with weak cellular signals.
• Bluetooth Interference: Although it’s less likely, Bluetooth devices in close proximity to your phone could cause interference. Try turning off Bluetooth temporarily to see if it makes a difference.
• VoIP Interference: The security system might use VoIP technology which can sometimes have compatibility issues with certain phone settings or networks. Again, this would be something to discuss with your building's management or the security system provider.
• Alternate Contacts: For deliveries, you might want to provide an alternate contact method or set up delivery instructions that don't rely on the buzzer system.

I would suggest having the building management coordinate with the security system provider to troubleshoot this issue further. It might be useful to test the system with another phone or network to see if the problem persists.