i know you are all growing citrus way longer than me, but for me i think the problem is constant overwatering my citruses. I now think that the size of the container is the most important factor, way more important than fertilizer or a good medium. I have 5 plants, and the 3 with the "highest" containers are losing the most leaves, 2 of them are naked, the other one got a few leaves left.
I really mean the height of the container, not the size, even though the size should be almost the same as the size of the rootstock.
whenever i planted a citrus in a way to big container it died ._.
I also think all this only applies when the soil temperature is less than 27°C (80°F) , what it definetely is in winter in my zone (19,5°C = 67,1°F for my pots).
but i could also be very wrong, iam not sure at all