After update 2.4: I don't have SALE BADGE

And what was _price for that one? Or was it missing?

nope. regular price 1000 | sale price 799
all prices are saved, but regular price doesn’t show in shop, and product doesn’t looks like is on sale, because sale price is as normal.

I got that part, but you showed:

<wp:postmeta>
<wp:meta_key>_regular_price</wp:meta_key>
<wp:meta_value><![CDATA[967]]></wp:meta_value>
</wp:postmeta>
<wp:postmeta>
<wp:meta_key>_sale_price</wp:meta_key>
<wp:meta_value><![CDATA[799]]></wp:meta_value>
</wp:postmeta>

In that example, what was under

<wp:meta_key>_price</wp:meta_key>

sorry, I didnt realize that is more than one price record!

<wp:postmeta>
<wp:meta_key>_price</wp:meta_key>
<wp:meta_value><![CDATA[799]]></wp:meta_value>
</wp:postmeta>

ok. so…._price showing sales price, but why :O when I import csv suite automatically attribute to I think correct record.

Thats perfect. _price should be equal to sale price i this case. What is the link to this product?

https://robocam.info/sklep/dws/plyn-rd-095-1kg-po-terminie/

Those meta values are fine now. Whats odd is your page has no indication of this. Our function should be returning true for you:

https://github.com/woothemes/woocommerce/blob/master/includes/abstracts/abstract-wc-product.php#L725

Are you sure no other plugins or the theme are filtering on that what I linked to?