That’s not your post, and its a year old.
I am having the same issue. I am on version number 184.108.40.2062.
The HSN/SAC columns are not auto-filled in sale/purchase invoices.
They are not printed on the invoices even if I manually fill the HSN/SAC columns.
I have set the localization to India and all the necessary HSN/SAC fields are filled for both inventory and Non-Inventory items.
Still, there is a problem with it.
I am using Server Edition with Version 220.127.116.117
Inventory Item with HSN/SAC,
Sales Invoice Edit screen, where the HSN/SAC is Empty.
Final Sales Invoice, where Localisation HSN/SAC is not getting fetched.