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 (
    102379, 102378, 102377, 102376, 102375, 
    102374, 102373, 102372, 102371, 102370, 
    102369, 102348, 102346, 102345, 102344, 
    102343, 102342, 102341, 102340, 102339
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00065

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
102339 4M 0
102340 4M 0
102341 4M 0
102342 4M 0
102343 4M 0
102344 4M 0
102345 4M 0
102346 4M 0
102348 4M 0
102369 4M 0
102370 4M 0
102371 4M 0
102372 4M 0
102373 4M 0
102374 4M 0
102375 4M 0
102376 4M 0
102377 4M 0
102378 4M 0
102379 4M 0