Many different reasons can explain why the image of the other user gets frozen during a video call. If this happens, sometimes the best thing is to hang up and call the person back again.
The image on the video call can freeze because of many factors. Some of them are:
The person received a double call and is no longer on the call
The person left the conversation to navigate on their phone
One of the two phones has a bad reception
When placing a video call, always try to make sure you have a good connection and that both parties are active on the conversation.