Multivariant fields missing in front-end

[Geppux]

Hi I have J 3.4.6 and VM 3.0.12.
I use Multivariant custom fields for many of my products and I noticed only now (I'm quite sure this problem there wasn't in the past) that, in the product page, the variants are not displayed correctly.
In this page, http://mulligan.it/it/attrezzatura-da-golf/set-di-ferri/callaway-xr-irons-detail.html , you can see that there is the "Composizione" and "Shaft" dropdown menu but not the "Flex" one... Any Idea of the cause?

Thank you, bye.
Giuseppe

[Geppux]

I tried also to use the standard beez template but I have the same problem...

[Geppux]

I noticed that I have this problem if the multivariant custom field has "show labels" set on YES; if I set to NO then I can see all the 3 dropdown menu... I don't think this is normal, is it a bug?