Hard to say without a pic, but I'd make sure the graft union is well-healed and there was at least one flush (prefer two) with mature (hardened and color-correct) leaves. I'm probably being more conservative than I need to be, but I repotted several mangoes in mid-winter and lost a few. All seemed healthy, the ones I lost were late-season grafts that only had one minor flush, with leaves that were small and still lighter green in color. I tried to not bare-root them, but it was largely unavoidable with the way they came out of the pots. Watching their leaves wilt and fall off while the trees slowly died in February was frustrating.