[cellarius]

You need to register variables to make them available in templates:
https://vborg.vbsupport.ru/showthread.php?t=228078

I thought you knew all that, since you're already doing it:

PHP Code:

$catb = vB_Template::create('bfc_download_cat_bit');
            $catb->register('cat_bit', $cat_bit);
            $cat_bit .= $catb->render(); 


You need to do the same as in the second line for $catb for $cid.