I do not think a replacement would fix it for him as I believe it is still a software problem that affects some people on this board.
For me it occurs when an iphone (X) tries to backup videos to the apple cloud and google cloud (my wife has it both enabled, it doesn't happen everytime, sometimes once in two weeks, the larger the files are the larger the chance for the hangup) or using youtube on an iphone (again, seems to be random).
It never occured with any other device and it certainly does not occur when the iphone is connected to the different router as it is now.
I'm getting the iphone for myself this month so I'd try to pinpoint it if I'm lucky.
Regards