At the beginning of episode 7 of season 2 (episode 32 on Crunchyroll), around 1:48, the colossal titan eats Ymir and one other person.
Given who the colossal titan is, it seems strange to me that he would have eaten someone without a purpose, but only Ymir is seen later.
Eventually, they run off on the armoured titans back and the second person is not with them.
Surely they could not have been digested in the short time the colossal titan was present, and they were swallowed whole.
Later on, when we see them in human form in the giant forest, no one besides Eren and Ymir are with them. Do we know who this person was?