404 on POST request checking stock on product page

[RobertoSV]

I've a weird problem here.

My website returns a 404 with this URL

https://mywebsite.com/gb/index.php?controller=product&token=714c22fcf2f5d11afb72cb37dcce2b04&id_product=1710&id_customization=0&group[2]=21&qty=1

But it works fine with the default URL without the language ISO code:

https://mywebsite.com/index.php?controller=product&token=714c22fcf2f5d11afb72cb37dcce2b04&id_product=1710&id_customization=0&group[2]=10&qty=1

This URL is called when I change any attribute in the product page like size or color.

I have tried to fix it in my .htaccess file without success:

RewriteEngine on
RewriteRule ^gb\/index\.php?(.*)$ /index.php$1 [L]

Anybody knows how to fix this?

Thanks