Host disabled video sharing

I conduct one-to-one meetings on Zoom with various clients. On occasions (not all the time), I cannot see the picture of one client when he joins my meeting. He says he can see the message 'host disabled video sharing'. On the occasions this happens, I send him a new meeting request and link and there is no problem. Sometimes we have to do this, and sometimes the issue doesn't arise and I can see his picture from the start. But I'd like to find out what the issue is as it wastes time at the start of the meeting if I have to email him another Zoom meeting request. I don't know what device he uses. Can anyone help me figure out what the problem is? I conduct 6-8 meetings per week on Zoom and only have the problem with one client, and not all the time. Thanks in advance.