Complex sentence: Julian was distracted by the presence of Yu Tsai, whom she is uncomfortable working with, at the casting for Zenchi, while Sang-in ended up overthinking everything and came off as uninspiring to both clients.
Split into simpler sentences: Julian was distracted by the presence of Yu Tsai, whom she was uncomfortable working with. At the casting for Zenchi, Sang-in wound up overthinking everything and came off as uninspiring to both clients.