I absolutely don't understand what is going on, it's like my part has broken into 2 separate pieces.

I attached a screenshot, this part was not imported, it was made in SW 2011.

There should not be a seam where the red circle is.

The widths of the two sections are exactly the same - 1 inch

And I made sure to make my sketch coincident with the line at the top.

No, in addition, I also cannot create a fillet on both top and bottom halves of this part.

I can create 1 fillet at the top and another at the bottom, but I cannot create 1 and select within it edges on the top half and on the bottom half

Why is this happening>?

Thanks,