Answer
Check for a missing grant on a specific underlying view — in one confirmed case, the permission set already had COMPANY_PERSON granted, but the sticky-notes feature specifically also needed COMPANY_PERSON_ALL granted, and granting the broader base view alone wasn't sufficient. The general lesson: a specific feature like this can silently depend on a more specific or additional view grant that isn't obvious from the headline permission options alone, so if a feature still doesn't work after granting the seemingly-relevant permission, check for a related but differently-named view that also needs to be granted.