Rafters on 24" centers with 1/2" OSB is very common under concrete tile. In California collar ties are usually installed only on every other rafter pair and that condition might mean that rafter pairs without collar ties could sag, but the ridges look uniform up and down the roof… they dont sag more in the middle of the span, in fact they seem to bow up more in the middle of the span. That would indicate rafters with extreme crowns.
With adjacent rafters crowned opposite or moisture-damaged sheathing sagging or bowing between rafters, the roof should look sort of rolling, wavy, rather than sharp, short ridges like that. No sign of moisture on the underside of the seathing? No bowing/sagging of sheathing between rafters visible from underneath?
Did the whole roof look like this or just this section?