Many shops I visit have their rulers hung the same way, have not heard of this happening before. Is their a heat source near them? Or has their been a lot of humidity? You can probably put them between heavy books or boards and flatten them back to the way they should be. Then I would be investigating the reason for it happening. Is the peg board flush against the wall? If the peg board is not flat that could be the problem. Use a long level and check. Your room looks great I hope you can figure out what caused the issue & fix it