Oh dear. Well, let's see . . . it's pretty clear you're not getting the same temp in the middle as on the sides of the things you're baking. Cold middle . . . hmmm . . . is your oven gas or electric? If gas, there could be some clogged jets under there that aren't burning owing to lack of fuel. If electric, my guess would be that you have a bad element. A third possibility might be that there's some sort of buildup on the middle of the oven floor that's impeding heat transfer - or there could be a hairline crack in the oven somewhere in the middle of the floor or door or back wall - or the door itself might be a loose fit towards the middle (you can check this with the old dollar-bill-in-the-door that we use for fridges). Let us know what sort of oven you have and what you find in and under there. There has got to be a mechanical reason for this - and by George, if I have anything to say about it, it WILL be found!!!
(You'd never guess that one of my top two lid-blowers is recalcitrant equipment/machinery, would you?? Oh, the tales I could tell . . .)