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.company_id = 2 
  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 = 953 
WHERE 
  cscart_products_categories.product_id IN (
    8862, 8860, 10172, 8878, 10945, 8864, 
    8880, 8875, 8869, 8886, 8891, 10211
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00156

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_products_categories range PRIMARY,pt,product_id_idx,category_id_idx,product_category_idx,category_product_idx pt 3 156 Using index condition
1 SIMPLE product_position_source eq_ref PRIMARY,pt,product_id_idx,category_id_idx,product_category_idx,category_product_idx PRIMARY 6 const,mahm3t_cs443.cscart_products_categories.product_id 1
1 SIMPLE cscart_categories eq_ref PRIMARY,c_status,p_category_id,idx_category_id PRIMARY 3 mahm3t_cs443.cscart_products_categories.category_id 1 Using where

Result

product_id category_ids position
8860 480,948,950,953 0
8862 480,948,951,953 0
8864 480,948,950,953 0
8869 480,948,951,953 0
8875 480,948,950,953,956 0
8878 480,949,950,953 0
8880 480,949,950,953 0
8886 480,949,951,953 0
8891 480,949,950,953,957 0
10172 480,949,951,953 0
10211 480,949,951,953,957 0
10945 480,948,951,953 0