How are random woocommerce WP products selected?

Question

WordPress

Friends, I can’t understand how random products work,
for example, this shortcode changes products (well, very rarely and constantly in the same sequence.
Why can’t random ones be taken all the time when loading? Just filtering new products every time.

[recent_products attribute ="brand" filter="Omnilux" orderby="rand" per_page="8"]
I am attaching a video of how random products work. Is this how it should work? or is it a feature of mine.
https://yadi.sk/i/8sb_yHU3huMchA

Just in fact I thought that rand is always random, but it turns out that I have more than 500 products and the
shortcode above takes 3 rows of products by 8 and spins them in a circle.orderby="rand" limit="8" ]
Not random at all. The latest version.