Technology
One of the reasons can be due to a weak or unstable internet connection. Spotty connections disrupt the signal between devices, preventing calls from coming through.
Here's a classic mistake: your phone's ring/silent switch gets bumped to silent without you realising it. With no audible notification, it's easy to miss a call.
Another factor that could be affecting your iPhone’s ability to ring is having DND mode on. With DND enabled, your iPhone stifles sounds to prevent disturbances
If your iPhone is linked up with wireless headphones, speakers, or even your Apple Watch, incoming call notifications can get rerouted without you realising.
iPhone features intended to improve audio. Cases of WhatsApp calls not ringing can sometimes be caused by Phone Noise Cancellation glitch.