SELECT 
  cscart_products_categories.product_id, 
  GROUP_CONCAT(
    IF(
      cscart_products_categories.link_type = "M", 
      CONCAT(
        cscart_products_categories.category_id, 
        "M"
      ), 
      cscart_products_categories.category_id
    )
  ) AS category_ids, 
  product_position_source.position AS position 
FROM 
  cscart_products_categories 
  INNER JOIN cscart_categories ON cscart_categories.category_id = cscart_products_categories.category_id 
  AND cscart_categories.storefront_id IN (0, 1) 
  AND (
    cscart_categories.usergroup_ids = '' 
    OR FIND_IN_SET(
      0, cscart_categories.usergroup_ids
    ) 
    OR FIND_IN_SET(
      1, cscart_categories.usergroup_ids
    )
  ) 
  AND cscart_categories.status IN ('A', 'H') 
  LEFT JOIN cscart_products_categories AS product_position_source ON cscart_products_categories.product_id = product_position_source.product_id 
  AND product_position_source.category_id = 4 
WHERE 
  cscart_products_categories.product_id IN (
    99157, 99156, 99155, 99154, 99153, 99152, 
    99151, 99150, 99149, 99148, 99147, 
    99146, 99145, 99144, 99143, 99142, 
    99141, 99140, 99139, 99138
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00082

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_products_categories range PRIMARY,pt pt 3 40 Using where; Using index
1 SIMPLE cscart_categories eq_ref PRIMARY,c_status,p_category_id PRIMARY 3 toolboxdigitalshop_dev.cscart_products_categories.category_id 1 Using where
1 SIMPLE product_position_source eq_ref PRIMARY,pt PRIMARY 6 const,toolboxdigitalshop_dev.cscart_products_categories.product_id 1

Result

product_id category_ids position
99138 29,4M 0
99139 29,4M 0
99140 29,4M 0
99141 29,4M 0
99142 29,4M 0
99143 29,4M 0
99144 29,4M 0
99145 29,4M 0
99146 29,4M 0
99147 29,4M 0
99148 29,4M 0
99149 29,4M 0
99150 29,4M 0
99151 29,4M 0
99152 29,4M 0
99153 29,4M 0
99154 29,4M 0
99155 29,4M 0
99156 29,4M 0
99157 29,4M 0