Definitely a jammed / failed shutter curtain blade.
Contact Canon to arrange for service.
The camera has a mechanical focal plane shutter with two "curtains" or "doors" that slide open and closed like window blinds... but hinged on one side. Each "blade" of the blind folds into it's adjacent blades. But if a blade jams, you'll get a gap in the curtain that looks like a horizontal bar ... but coming to a point on one side (because that's the side where it hinges).
Here's a video that shows how it operates in slow motion:
This is not the sort of problem you would want to try to fix yourself. Your best course of action is to contact Canon service and arrange for a repair.
The shutter mechanism is one of the very few parts in a DSLR camera that does wear out with age and eventually needs to be repaired. The number of shutter actuations can vary wildly but most cameras have a shutter life estimated to be around 100,000 actcuations (some models have shutters rated for higher counts). Sometimes a shutter fails sooner... sometimes later.
Tim Campbell
5D III, 5D IV, 60Da
