Usually in wet stressed years it is not uncommon for Crabapples to shed there leaves early to protect themselves. Hot humid conditions can cause this as well. As far as flowering again there may be dormant buds that never pushed due to being stressed. The tree should be using it's energy now to form the buds this fall for spring. Be sure you see next years buds about November. If the leaves are diseased you may want to rake them up and discard them in order not to spread any viruses. Fertilize in the spring and do any necessary pruning after it flowers.
I don't know. But i will say i was.noticing that apple trees have been losing their leaves, and we were guessing that the erratic rain patterns were a possibility. Tons of rain- then no rain. Don't get a continuous light sprinkle these days..
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