Hi @Ben_Rix ,
I am certainly willing to help to the best of my ability. However I am afraid, I am not yet clear on the exact scenario that the app has.
Your entire expression that you have shared is not clear and probably has syntactical errors.
In general, based on your description so far and my understanding, your expression could be something like
IFS( AND(IN(“Scheduled”, [Related Case Sessions][Attendance] ), COUNT(SELECT([Related Case Sessions][Date], [Date]<TODAY()))>0, “Scheduled”…
This expression will select “Scheduled” if any of the child records’ [Attendance] column has “Scheduled” status and any of the child records’ [Date] column has a date lesser than today.
It is not clear how you have constructed the IFS() expression, so my shared expression mainly takes care of IFS() condition.