We are unable to reproduce this issue. 

User settings (First check) 

• Silent mode (Mute switch): On iOS devices, many audio engines block sound when the physical mute switch is on, unless the audio category is explicitly set to playback.
• Focus / Do Not Disturb: Check whether Do Not Disturb mode or a focus profile is suppressing audio output. 
• Bluetooth connections: Sometimes a phone is connected to headphones or a car system in another room, causing the sound to "disappear". 

Still not resolved? 

• Try the following: Check that the volume is turned up in the app and on the device. 
• Test whether other apps (YouTube/Spotify) are producing sound. 
• Force the app to stop and restart it. 
• Check whether an update is available for the operating system. 
• Install the app on another phone belonging to a family member.