I've been growing this avocado indoors in my office for almost 2 years now, it was doing alright under the ceiling lights, unfortunately my desk is nowhere near a window.
It had begun to outgrow its pot so I repotted with some minor root pruning.

It did well at first, growing several healthy leaves. Then suddenly it began to show signs of salt accumulation so I began adding a small amount of vinegar to the water and made sure to water until it drained from the bottom.

That seemed to correct the problem for a while but I recently noticed that the root ball was not getting any water, the soil was having a really hard time absorbing moisture and it would just run down the inside edges of the pot. I watered a few times with a drop of soap until the soil was accepting water again.

In my overzealous attempt to moisten the soil I think I overwatered it, two leaves began showing rapid browning and became crispy around the edges, I allowed it to dry out slightly before watering again.

At this point it had no leaves left but had begun to show signs of backbudding along multiple points, it looked like there would be at least 5 new shoots of foliage until yesterday when I noticed that the new shoots had gone limp and were browning.

This always seems to happen to my Avocados at around the 2 year mark. Why can I never grow Avocados older than that?

Thank you for any help!