How to include price field data in a Contribution Thank You letter
It doesn't work because $lineItem is not set in the template, you'll have to loop thorough $contribtuions and use the API:

{foreach from=$contributions item=contribution}
{crmAPI var='result' entity='LineItem' action='get' contribution_id=$contribution.id} 
  {foreach from=$result.values item=lineitem} 
    {$lineitem.label} // Price field label
  {/foreach}
{/foreach}


Please note: this works fine generating ThankYou's with one contribution per individual.

Related topics for more details:


How can I use custom tokens when grouping Thank You letters
Contribution Note Smarty Variable


Let me know if that helps.