@Louxue 

Theoretically, the Deco M5 won't affect the performance of the smartbell, instead, it just provides wireless network for them to get internet. We can do some troubleshooting to locate and fix it.

You can double check the audio function on the smartbell system first. 

Meanwhile, you can hard reset and reinstall the smartbell to give it a shot.

Still the same, you can contact the tech support of the smartbell to get some help cause they are more professional about their product. 

Good day. 

@Louxue 

Thanks for your reply, below are some suggestions but we are not sure whether they can help you solve this issue. 

1. With smartbell connected to the TP-Link wireless network, please turn off the mesh technology via the Deco app.

2. If the Deco works in router mode, please disable fast roaming and setup application QoS as standard and clear all the high priority rules to give it a go. 

3. Try to turn off the antivirus software on the Deco app. 

May it help and have a good day.