Won't as much as a flat spot but is narrowing of the v-belt backbone. Other words it may not be 1/2 wide anymore in one or more spots and it goes around a v-pulley the belt drops further down in the groove then must jump back up as it returns to the normal width. What I call a belt burn where didn't move when another was locked up. Just missing fabric in places can cause belt changing lengths.
Hope this makes sense.
