GrimLore
Bonsai Nut alumnus... we miss you
As Sandy said and as well as the tree having some issues last year I would suspect a weather issue as well. We have been having those unusual cold nights too and I am hoping tonight is the last one for the season. What I have noticed on what is left here the plants requires far less water and stay damp far longer. That is a perfect combination of weather and moisture to inspire fungal problems. Being confident you have done all else correctly; Copper is my go to along with less water and things respond well. I might add that it also has been rather windy so although the substrate may look dry that is just the top.
Grimmy
Grimmy