[Plugin: Woocomerce] product-tag producing 404 Error pages

Hi guys,
I have a woocomerce sotre and everything seems to go pretty well except the prudct-tag issue.

As soon as I add a product I am also adding some product tags to it.
The problem is after I am saving and publishing my product and view it on my store, I click on one of the product tags and then I am getting 404 page.

Although some product tags are working, I have a 2000 product tags or so but the majority of it (almost all of it) are producing 404’s.

Can’t figure out why. I’ve tried to change the permalinks as well several times but it didn’t work for me.

I am using Woocommerce 2.3.13 (not the new version) but I know it’s irellevent. this problem is 4 months old.
My template is: Flatsome v2.5.5 with child theme.

I am a rookie programmer but dont have problem to handle with some code.

Thank you all.
Asagf