Hi Gaston,
The slider plugin does not have any code that would affect only the viewing of WooCommerce products. It does have an option to pull the info from a WooCommerce product to create a slide, but this shouldn’t affect the single post display of the WooCommerce product itself.
If you disable the Ultimate Slider plugin, does the admin bar come back when you click on “view product” for a WooCommerce product?
The past issue was actually a conflict with the lightbox that was included with the slider. But that issue has been resolved for quite some time now. There is currently nothing in the slider plugin that should cause the admin bar to disappear.
Do you have the latest version of the slider plugin? If not, please upgrade to the latest version.
Also, are you using the Ultimate Lightbox plugin? If so, please make sure you have the latest version of that plugin.