At first glance it would appear that the left blade is too short. The blades do not over lap, the mower deck is set at a slight angle so that you get 100% cutting. I would start with the left blade, it is either too short or really dull/damaged.

Normally the blades should overlap a little bit respectively the area they are supposed to cut. Check the alignment of the two blades, maybe you find the problem there. It′s no more than an idea because it′s hard to "telediagnose" without seeing the patient. Maybe you hit or ran over something (without noticing even) which offset the left blade mounting a little bit?

I own a Cub Cadet 2000 series tractor with a 50in. mower deck and when Im mowing grass there is a 3 inch swipe between the left and middle blades that does not get cut. Ive tried going slow and the problem still persists, can anyone tell me a reason or at least an idea as to why is would do that.