Something in the mesh algorithm has resulted in a loss of mesh area. If this is a larger chunk - you can often see this as a hole in the analysis mesh. However the increment seems quite small - so it may be difficult to find. But it has indicated which area is having an issue, so you just have to work on area F2 to make sure all of it's joints line up with neighbouring shells.

I don't think that deck sections should be meshed though - unless I am incorrect. Deck sections should be four node quads that just distribute load to beams using tributary width.

It seems like you have a lot of ETABS questions about real projects - I would make sure you have someone who can oversee this kinds of questions because waiting for forum answers is going to slow you down dramatically.