Hi David and welcome. Here''s the database entry for your Annona. It says it is evergreen but "may be briefly deciduous". So the question might be, is it cooler at night where you are keeping this plant? Also, how much light is it getting. You are fairly far north, and a tropical fruiting tree needs a lot of sun and warmth to keep growing "normally".
Custard Apple (Annona cherimola)
Pretty much the same questions apply to your avocado plant. They do lose leaves regularly through the year so that would be more or less normal. But I would say keeping it as warm as you can, and giving it as much bright light (preferably direct sun) as possible will keep it happy.
Also it's fairly important to note that tropicals raised as houseplants in northern climes will certainly slow down their growth rate during winter anyway. So you need to fertilize and water more sparingly than you do in warm weather when you can grow your plants outside. Too much fertilizer or water (or both) when the plant is growing slowly can cause leaf tip burn and other damage.
