What is the ruling for a follower who joins the Imam during the second bowing (Ruku) of a prayer cycle?

Primary text

There are two possibilities regarding a follower who catches the Imam during the second bowing of a cycle. One possibility is that the follower misses that cycle entirely. This is argued because missing the bowing in a cycle is analogous to missing the bowing in any other prayer, thus invalidating that cycle for the follower. The second possibility is that the follower's prayer is valid because it is permissible to perform the prayer with only one bowing, and this suffices for the one joining late (Masbuq). Allah knows best.