Can't add sim to custom venue role

hi! I'm having an issue with custom venues where it won't let me add one particular sim. I'm trying to get this one sim to be considered a "student" role for a boarding school type of lot and it will let me add all the other sims I want except for him. Does anyone have any suggestions? Here's what I've tried:

• Trying to add a completely different sim to the custom role
• Using a different sim in other household to add said sim
• Removed my mods and started in a new save
• Kept my mods and did a completely different world
• The sim I'm trying to add does meet all the requirements and I've checked the schedule itself.

Nothing seems to work. Any help would be greatly appreciated! At this point, I'm assuming it's a game bug.

Thanks!