Ye like mentioned not all seeds have the same genetics. Usually when the upper growth slows down it means that its establishing its rootzone a bit further. You say you had rain, probably some wind as well, exposing the plant to such conditions will trigger a response such as increase the rootzone so its grasp with the earth is better and wont get damaged or uprooted by winds. After its finished adjusting itself for a better grip its gonna explode in upward growth. Its absolutely normal, i wouldnt worry ^_^