Perhaps over fertilized?
I did that a few months ago on a year old tree, learned the hard way. Half the tree lost its leaves and new growth died prematurely. No fruit yet so can't comment on that. I also had to trim the tips of the branches since they started to dry out. Luckily, a few months since, growth has restarted.
(My tree is outdoors so I can't comment on light being a factor for an indoor tree π¬)