2015 iMac issue

For those who can’t watch the video my mid 2015 5K 27 inch iMac has this extremely strange issue where when I plug in another device such as iPad iPhone iPod, it repeatedly connects and disconnect without any interference trust me the cable is fine. I’ve used this cable and other device devices and it has not done this. I even used my brand new USPA to lightning official Apple cord plugged it into an iPad cause I was gonna transfer data from one to another and it’s not working. It’s doing the same thing. Any ideas on what to do?