Calculated column not returning what I'm expecting

I am trying to determine from another column if their join time was in the morning or in afternoon. If a join time is AM and leave time is PM, then I want the calculated column to show "AM/PM"
The table context is each row is a record of a person joining a training.
The reason I want to do this is I want to determine how many distinct people were in the morning call and how many people were in the afternoon call.
So if a person joined in the morning and left in the afternoon, it means they were in both AM and PM sessions.

I wrote the following calculated column:

AM/PM Session =

SWITCH(

true(),

AND(CONTAINS('Activity Table','Activity Table'[Join Time], "AM"), CONTAINS('Activity Table','Activity Table'[Leave Time], "PM")), "AM/PM",

AND(CONTAINS('Activity Table','Activity Table'[Join Time], "AM"), CONTAINS('Activity Table','Activity Table'[Leave Time], "AM")), "AM",

AND(CONTAINS('Activity Table', 'Activity Table'[Join Time], "PM"), CONTAINS('Activity Table','Activity Table'[Leave Time], "PM")), "PM",

)

Join and leave time I made both of them text values, and the calculated columns are bringing back "N/A". What am I missing here?