Avocado yellow veins

Wodez starts with ...
Hey there
I have a potted fuerte avocado the has recently started to get yellow leaves. It starts at the base of the leaf and travels through the veins.
Also there is some small brown lines on some branches. And some cut branches seem to be dying back from the cut. I’ll see if I can add another photo.

Problem was first noticed 3 weeks ago. The tree was purchased about 2 months ago, repotted 6 weeks ago with a good potting mix, a handful of balances fertilizer and gypsum and plenty of drainage holes.
Tree gets full morning sun, midday sun through tinted polycarbonate roof and 1 hour afternoon sun.
Just stating summer here after having a wet spring, but tree has been under cover since I bought it.
There has been no new growth either.

Any help or advice would be much appreciated
Thanks

Pictures - Click to enlarge
Picture: 1