Because I kept getting this wrong, I asked Chatgpt: Can one use deber conjugated in El Pretérito Perfecto, followed by an infinitive to express in Spanish that something must have happened, as when making an assumption or wondering what must have happened? The response was: No—not if your goal is to express an assumption ("must have happened").
The pretérito perfecto of deber (ha debido) normally means "has had to" (obligation), not "must have" (probability).
