mute on whatsapp?

Hello folks,

I hope one of you can help us. My boyfriend and I sometimes talk on WhatsApp. I have an iPhone 15 and he has an iPhone 14. When we talk, I often can't hear him for 10 seconds, even though he's not muted. This happens every few minutes. Often, I just can't hear his audio, including any background noise. What could be causing this? Are there settings, or does anyone have another idea? Because it's incredibly annoying; I can't talk normally. Thanks in advance 🙂