There are two possible causes for this condition.
One is that the anaerobic metabolism of local muscles and other tissues increases when doing pull-ups, and metabolic products such as lactic acid accumulate there, so it can lead to a sore feeling.
Second, high intensity or incorrectly doing pull-ups may lead to external damage to the bones, muscles, tendons, and nerves around the shoulder joint, resulting in strain, inflammation, and compression, leading to osteoarthritis, tendonitis, fasciitis, and even fractures and dislocations that cause pain.