by the way,I found in my IOS 15 setting 「safari =>Advanced=>Experimental Features=>NSURLSession WebSocket 」is default On, in IOS 14.X is default Off,I'm not sure it has an impact.

My problem is :if I use IOS 15 iphone send message to WebSocket server ，server receive multiple frame ，but in IOS 14.X only receive one frame. For example a message 「 I have an apple」， in IOS 15 my WebSocket server will receive 「 I have」+「an apple」,must receive twice or more,but in IOS 14.X my WebSocket server receive 「 I have an apple」 just receive once