Solution: I have been judging yeast breads at county and state fairs
for 25 yrs, and bake bread 2-3 times a week.
Those that taught me evaluation techniques always said that wrinkling
on a loaf top was caused by cooling in a draft or cooling too
rapidly. (375F to cool room temp) Think about human skin. When you
are very cold, your skin contracts and your ring slips around
easily. My loaves have always wrinkled, so I tested this by taking a
loaf out of the oven & immediately moving it outside on a 100F degree
day without a breeze. It still wrinkled a little.
Later I ran into a professional baker with a Baking Science
degree. She said that if the crust is tender you always have
wrinkling. If the wrinkles are more than the average, you might try
cooling in a warmer, draft free location. This baker totally changed
my thinking. I now expect a tender crust when I see wrinkling. You
did not tell us the recipe and technique, but I am guessing you are
not talking about a crusty artisan style loaf, but instead, a soft
American style bread loaf.
Joyce