There are several reasons why a dog could all of a sudden begin eating poop such as medical conditions including enzyme deficiency, pancreatic insufficiency, intestinal malabsorption, and GI parasites.
It's a good idea to have the dog checked out by a vet just to be sure nothing is wrong with the dog if it just suddenly begins eating poop including it's own poop.
If the dog has started eating other animals poop then it should be stopped because the dog could get sick by the poop being infected.
But the dog eating it's own poop is not harmful to them.
Still if the dog is eating it's own poop you can add some meat tenderizer or a tablespoon of canned pumpkin to the dogs food and it will cause the dogs poop to taste horrible and the dog will stop eating it's own poop.
Also start cleaning up the dogs poop after you notice poop on the ground to keep the dog from eating it's poop.
Dogs who are mostly on a dry dog food diet will usually have an enzyme deficiency so the start eating poop to make up for that enzyme deficiency.