The issue wasn't with the growing text view but rather with the UITableView auto-scroll which doesn't seem to fire when detecting the return key. So my solution was to check for the new line character manually and to force a scroll to the bottom of the cell.
- (void)growingTextViewDidChange:(HPGrowingTextView *)growingTextView {
NSString *text = growingTextView.text;
NSInteger endIndex = text.length - 1;
if (endIndex >= 0 && [[text substringFromIndex:endIndex] isEqualToString:@"\n"]) {
NSIndexPath *indexPath = [NSIndexPath indexPathForRow:0 inSection:textViewSection];
[self.tableView scrollToRowAtIndexPath:indexPath atScrollPosition:UITableViewScrollPositionBottom animated:NO];
}
}