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 = 29 
WHERE 
  cscart_products_categories.product_id IN (
    37261, 37189, 37186, 37157, 58968, 40532, 
    40347, 40346, 40345, 40344, 37060, 
    40530, 40524, 40523, 40522, 40521, 
    40520, 40354, 36734, 36533
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00046

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
36533 29,4M 0
36734 29,4M 0
37060 29,4M 0
37157 29,4M 0
37186 29,4M 0
37189 29,4M 0
37261 29,4M 0
40344 29,4M 0
40345 29,4M 0
40346 29,4M 0
40347 29,4M 0
40354 29,4M 0
40520 29,4M 0
40521 29,4M 0
40522 29,4M 0
40523 29,4M 0
40524 29,4M 0
40530 29,4M 0
40532 29,4M 0
58968 29,4M 0