Probably a "New Bike" adjustment gremlin.
Nice ride! As to the numbness in the thumgs, that kind of goes with flatbars. Get some bar ends and/or some Ergon grips and your hands will be a lot happier, and also get some padded gloves, they help too.
Also, relax your grip and shake the hands out every oonce in a while.
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"We can judge the heart of a man by his treatment of animals." - Immanuel Kant