Complex sentence: Disney did not focus on the project again until the autumn of 1935; it is thought that he may have doubted his, and his studio's, ability, and that his trip to Europe that summer restored his confidence.
Split into simpler sentences: Disney did not focus on the project again until the autumn of 1935. It is thought that he may have doubted his, and his studio's ability, and that his trip to Europe that summer restored his confidence.