I agree, in a ton of images, its never happened once with my 5D MK IV, or for the other hundreds of thousands of images on cameras before it. When its occasional, like once every 20,000 images, its probably a memory card, but you ruled that and other issues out, I'm glad your replacement is as it should be.
I'm glad it worked out for you.
Nothing more frustrating than a new camera not working straight out of the box.
Especially as a wedding photographer you need to be sure its going to work.
Glad the new one is working.
It's a great camera (of course Canon could have it made it better - but that would make this forum very boring).
You'll love it.