The Bonanza is fuel injected (In real Life) however it is possible that the MSFS model is configured for a carbureted engine.If that is the case you could be getting carb ice. Next time try to apply carb heat and see if it restores the power. You will probably need to use a binded key stroke to apply the heat as the Bonanza should not have a carb heat control, being that it is injected in real life.