Core Spotlight searching only for title

I just adding a way to donate my app's data to Core Spotlight using CSSearchableIndex, but I'm finding that spotlight is only searching for the title of the CSSearchableItem I create. I know the index is working, because it always finds the item through the title property, but nothing else.

This is how I'm creating the CSSearchableItem:

- (CSSearchableItem *) createSearchableItem {
    
    CSSearchableItemAttributeSet* attributeSet = [[CSSearchableItemAttributeSet alloc] initWithContentType: UTTypeText];
    attributeSet.title = [self titleForIndex];
    attributeSet.displayName = [self titleForIndex];
    attributeSet.contentDescription = [self contentDescriptionForIndex];
    attributeSet.thumbnailData = [self thumbnailDataForIndex];
    attributeSet.textContent = [self contentDescriptionForIndex];
    
    CSSearchableItem *item = [[CSSearchableItem alloc] initWithUniqueIdentifier: [self referenceURLString] domainIdentifier:@"com.cjournal.cjournal-Logs" attributeSet:attributeSet];
    item.expirationDate = [NSDate distantFuture];
    return item;
}

There's a lot of confusing tips around which say specifying the 'textContent' should work, and/or setting the displayName is essential, but none of these are working.

Is there something I'm missing with my setup? Thanks.