Hi, we have a avocado plant grown from seed, its about 1 year old. Its been growing really well, until recently when all of its leaves started to gradually turn brown and fall off. I thought it was dying, but it continues to shoot new growth from the top (as in the pic) but the new leaves just keep dying and falling off.
I've tried to research what the problem can be, but cant seem to work out what it is.
It was originally grown indoors, put outside for the summer, and now is back indoors as it starts to get cold. I would say it started to turn and loose its leaves towards the mid/end of summer?
Its got very long and spindly because of the leaf loss, it sits in a good spot in the window with plenty of light...
Any advice would be greatly appreciated!

Thank you