Some Reasons Why Cakes Sink or Fall In The Middle:

 Cakes will sink or fall because:

1). Overbeating – too much air is incorporated into batter.

2). Underbaking - Oven temperature too low and/or too short a baking time.

3). Over or under measurement of liquid or under measurement of flour.

4). Using too small or large of a baking pan.

5). Moving or jarring cake before sufficiently baked or opening the oven door before cake sets.

Note: Only open oven door if absolutely needed, one-half to three-quarter's way through baking.

6). The most common error has to do with the oven temperature. Make sure you have an oven thermometer to test your oven for accuracy.

7). Depending on the recipe if you fold in egg whites, if not beaten fully or folded in too harshly, the cake could fall.

8). Even creaming the butter and sugar too much or too little can cause problems.

There are a number of reasons to why your cakes may be sinking after u take then out theses are as follows:

The cake may not be cooked for long enough

Your oven may not be the correct temperature so its recommended that you test it with an oven thermometer!.

also the oven door may have been opened before the cake has set causing the cake to collapse!.

The mixture also may not have been beaten thoroughly enough or there might have been too little flour or too many eggs