The recipe calls for a square pan, but I use a round cake pan. Every time, my cake complete deflates in the middle and looks like a swimming pool. Why would that be? Would the square pan really make a difference?
First, the area (number of square inches or mm) should be close in the 2 pans.
But there are many other factors that influence baking. Is your oven temperature accurate? It's helpful to use a thermometer to check, as many ovens are not calibrated correctly.
Is the recipe from a good source? Are you following it or making critical changes? Baking is chemistry -- if you change something, you will not get the same results.
Can you provide more detail?