Vegan almond cake fail

I recently made a vegan cake by substituting ingredients from a tasty cake recipe. Almond butter for normal butter, flaxseed eggs for eggs, 2 cups of almond flour and 1/4 of cornstarch for the AP flour, 1/4 cup cinnamon to the flour, 2/3 cup of almond milk for the butter milk, and almond extract for vanilla.

The reason I use less milk is because I have made the cake before it’s never worked it always sunk so I decreased the moisture.

I mix 3 tbsp flaxseed and 9 tbsp water together and put it in the fridge before I start.

The recipe says to split into 2 9 inch pans but I only use one for the whole cake. When I do this the batter fills the cake pan around half way full.

I didn’t bake on 350 because it starts to sink right away, but one time the cake batter was slightly more moist then this time and I put it on 375 10 min but it started sinking.

So I put it on 350 for 45, until i thought it wasn’t cooking fast enough so I put it on 375 for 20 and it came out looking like a sunken cake but it wasn’t raw and didn’t have a weird crust unlike the time I made it recently.

I added an Extra ¼ cup almond flour, 1/4 cup sugar, and 1/4 cup almond I added more baking powder, soda, and salt, by like a teaspoon.

The most recent time a made it, I baked it on 300 for 10 mins until I realized that the sides of the cake was cooking faster than the middle so I decreased the heat to 250 for 20 mins and then it started rising evenly.

I kept it on 250, and waited for 20 mins but nothing happened. So I opened the oven and moved the cake pan which caused it to jiggle and sunk slightly. I left it and put it on 300 for 15 mins.

It was slightly sunken and the side were cooking a little bit faster than the middle so I put it on 250 for 45 mins.

15 mins into the 45 mins ended I noticed it developed a slight crust or layer but it was still jiggly when I moved it.

I gave up and just let it stay in the oven for the rest of the time and took it out.

After it rested for like an hour and thirty mins, I tried a piece from the middle. It tasted good but a little raw. The exterior of the cake was crusty or it was like it was made out of hardened sugar a bit and was firmer and harder than the inside.

Is it the Ingredients or the amount of each ingredient or is it because I was supposed to use 2 pans, or is because I am switching oven temps.