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?