The eye flick in the first gif means something so important. It’s Bucky’s gut, his feelings, his brain telling him that there is something he should remember about the man in front of him, specifically the name he called him—“Bucky”. It registers somewhere inside of him, even if the memories connected with the emotions refuse to come forward.
But they start to in the vault. Those memories, the things that are stored somewhere inside Bucky’s mind, deeply buried under years of programming and abuse and torture, start to leak out and manifest. Look at the haunted expression on his face, in his eyes, even in the way his mouth hangs open like he doesn’t have the will to close it. As the Winter Soldier, he knows he’s not supposed to be feeling the emotions that are running through him now. More importantly, the images, the voices, the recognition, that are flashing through his mind make no sense to him. He is a soldier, nothing more. There is not supposed to be anything other than his mission. Now there’s more—a lot more.
Bucky can’t make sense of it. Everything is jumbled up inside his head, snippets of loyalty, love, fear, and then nothing. His tortured expression is so heartbreaking because you literally see everything falling apart for him and he has no idea what to do with any of this. (once again, we need to thank Sebastian Stan for putting so much of his heart into bringing this character to life)