How to get interest group's teacher to substitution
Teachers in interesting groups usually have their lessons entered in individual timetables, not in a regular timetable. By default, lessons from individual timetables do not appear in the substitution. To do this, in Substitution, select Settings and then Advanced. Check the "Individual teacher's timetables - substitution" setting here.
Such teacher then appears in the list of teachers that can be added to the substitution.