Hi,
Thanks. I know what the problem is. When I tried to reproduce the issue on my end, I couldn't because I had other modifications included for the support of variants data, which are scheduled for the next version of HikaShop.
The current version of HikaShop actually doesn't support the indexing of variants data.
The indexing of the product_code specifically was another problem I found out but both the change I made previously following this thread, and the changes prepared on my end for the next version of HikaShop are necessary to be able to search a variants code.
Here is attached a modified installation zip of the finder plugin to be able to index variants which contains all the modifications.