Hey, Sorry for the delay, must have missed to answer.
It was reported to me and I checked your save already, Everything is fine so this isn't a bug, the only problem is that this isn't visualized in this interface.
View attachment 3309201
This is where the missing man is.
So once Umah's quest is continued he will become available again.
By loading your save I noticed some problems with Dasan's daily routine (due to the timetable changes I made in 0.5.7.0). I've just worked on that and it will be fixed in the next update.