I found the reason why the button “Add to Cart” in product details view is dissappeared. The button is inside <ul id="hcProductActions" class="hc-actions dnnActions dnnClear"> and inexplicably hotcakes dinamically add the style display none. See below the html result:
<ul id="hcProductActions" class="hc-actions dnnActions dnnClear" style="display: none;">
I've solved deleting the id="hcProductActions" to the _ProductDetails.cshtml view.
But why this happening?
Furthermore, at the top of the screen, I can now see a summary bar of the selected product with Views, Added To Cart, Purchased statistics but all is without any data and with a bad layout.
Are this bugs?

Well, it is definitely a bug!
I've tried to install a clean Hotcakes Commerce 03.01.00 Install Packages and the Add to cart button is not visible! I have already written in the previous post how to get around the problem but this is a bug and we should know more about!
For now the previous install version 3.0.1 work fine but it is no more available here and not even on github! this too would require a clarification to the community!
Thanks

a more in-depth analysis of the problem led me to find the javascript file responsible for the disappearance of the "Add to Cart" button, it is $actions.hide(); in the function EvaluateSelections() of the Product.js file
The same js function on HCC 3.0.1 work fine!
Is this an error to report on github for 3.1.0 HCC version?

I have a major update on this and other problems started after the upgrade!
I'm working on a multilingual website, if I disable the other languages ​​and leave only one of them active, everything seems to work fine.
As soon as a second language is rehabilitated, the problems reappear.
[b]so this is definitely a multilingual problem![/b]
Before opening an issue on github I'm waiting to know if others have this problem and if they have solved in any way ... I hope I'm not the only one in the world to have tried HCC 3.1.0 in multilingual web site!