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 = 6 
WHERE 
  cscart_products_categories.product_id IN (
    99275, 99272, 99262, 99261, 99258, 99217, 
    99132, 99129, 99124, 98903, 98630, 
    98626, 98625, 98566, 97667, 99274, 
    89234, 99131, 98519, 99123
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00054

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_products_categories range PRIMARY,pt pt 3 20 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
89234 6M 0
97667 6M 0
98519 6M 0
98566 6M 0
98625 6M 0
98626 6M 0
98630 6M 0
98903 6M 0
99123 6M 0
99124 6M 0
99129 6M 0
99131 6M 0
99132 6M 0
99217 6M 0
99258 6M 0
99261 6M 0
99262 6M 0
99272 6M 0
99274 6M 0
99275 6M 0