Also have a plum tree with one apricot branch grafted on. Not many apricots this year. Not sure why? Don’t know if birds got them, late frost or what?
Did they flower but did not set fruit? It could be a mineral deficiency. Lack of boron will do that. Did they over produce last year? Were babies and you let them produce fruit? Got severely stressed in any other way? If so they can be recovering from that.
I think I remember both blooming…the apricot branch and the dwarf nectarine tree.
I will try to find some boron supplements for next year and try it.
For boron as miniscule amount of borax would do it. Something like 1/8th of a teaspoon in a gallon of water. Apply as the flower buds begin to swell.
I’m not one to suggest supplementing without testing first but at that concentration it should not hurt and you probably already have borax laying around