Looks like dense soil with a high clay content and the tree is in a bit of a hole. If so did you loosen the area around it? When you plant trees flush or proud or with a shelter does the same the same thing happen? Most fruit trees are not fans of puddles/wells and if fertiliser is accumulating in a ring around the stem it isn't ideal also.
Of course the area around it has loose soil. The soil ph is indeed high but this tangelo compaired to the other citrus i planted yuzu, pomelos etc is doing a lot worse.
Yesterday i saw many buds starting to grow. So maybe it will be healthy again soon.
My only option was to put it in a hole like that.
Because of the slope and the fast draining water not even weeds grow there, unless i do what i have done