I had a limb break on a new compound bow once. I'd shot it maybe 40-50 times. Drew it back and heard a tearing noise. I actually checked my clothing, as I thought a seam had ripped.
I shot the arrow with no noticeable changes. I drew again and heard the noise again. Let the string down and found a limb was in the process of breaking! It looked similar to your limb, but was still attached by about 1/2 the thickness.
I would imagine the stress on the crossbow limb at full draw would be much more than a compound bow, so it probably broke so quickly there was no audible warning like I had.
The dealer said it was rare for one to break, but it did happen on rare occasions.
Luckily he had a new set of limbs in stock and had me shooting again within an hour.