During the meeting, an unexpected issue came up that required immediate attention.

came 是动词 come 的过去式，come 的基本意思是"来、到达"。 up 是副词，表示"向上、出现"的意思。 came up 是一个短语动词，字面意思是"上来"，引申为"出现、发生"的意思，特别指突然或意外地出现某种情况。