Reduce baking temp,if it sinks from middle& of it doesnt rise high overall then u r over beating the batter.Try cut& fold method.
Try and even out the batter. Wrap a damp cloth around your cake tin and then put it into bake. That should help
I think u r overbeating the batter. When u add the flour incorporate it slowly,gently mixing after each addition. &only mix till the batter is uniformly combined.Making sure u dont overbeat the batter. It'll rise to the highest.