Planted cimmzam ash tree dying

Hello, Wondering if anyone has any advice on where to go from here. We planted this cimmzam ash tree (photo 1) in October 2024 (photo 2). Seemed to be doing alright, but hadn’t grown like we expected it to. In march 2025, the leaves started to brown on the ends (photo 3) Now it seems to be dying completely (photos 4 and 5). I don’t see any evidence of borers, or black spotting.

We planted it with a mixture of the soil from the ground, compost from bunnings, and a fertilizer from bunnings. Dug the hole probably 2x the size of the pot it was in Because this was planted near the bore,we put a plastic sheet around the perimeter of the hole. So below the surface is a barrier about .5m deep to encourage the roots to grow down. We watered it a bit every day at the start, then went down to every other day, then 3x per week when we got our water bore fixed, so it just got the spray from the lawn sprinklers that come on automatically 3x per week.

When it started to look bad, I checked the soil and it seemed consistently moist.

Could this just be root rot? Is there anything I can do to save it or is it dead? Did the plastic barrier interfere with its root growth?

I appreciate any advice!!