I have inspected your store.
The misbehavior in question caused by your WP theme called 'multidesign' and the use of a custom .pageSlide() function in it. That function wraps the whole page body with an additional element, such wrapping re-executes all the scripts in the body of the page, and hence you get 2 sets of Ecwid widgets on the page. Basically, using that .pageSlide() function in its current for is incompatible with Ecwid widgets. Since only 1 Ecwid product browser can be active on a page, the last one that is being added becomes visible, so you see 2 category widgets and one product browser (another one is forced to be invisible).
The most correct way to fix it is to get rid of .pageSlide() function inside that page or on the website at all. The exact code that does call that function looks like this:
Code:
<script>
$("#allpage-login-top").pageSlide({ width: "334px", direction: "left"});
$("#allpage-signup-top").pageSlide({ width: "334px", direction: "right" });
$("#allpage-search-top").pageSlide({ width: "350px", direction: "left", modal: true });
$("#homepage-login-button").pageSlide({ width: "350px", direction: "left" });
$("#homepage-signup-button").pageSlide({ width: "350px", direction: "right" });
</script>
Most probably you can find it in one of the files of your current WP theme. To prevent it spoiling your shop page you can possibly remove that code, but this will remove the effect of the Login, Signup, Connect and Search buttons - they will stop working.
So, a possible workaround instead of removing that function call would be to include a special code directly after the Ecwid code into your store page. This code disallows adding any more Ecwid widgets into the page, so there won't be any duplicates. The code reads as:
Code:
<script>window.xAddWidget = function() { return false;};</script>
It should be added into the source of your shop page in WordPress (WP Admin → Pages, select your page and click Edit beneath it, then make sure to switch editor to HTML mode with a tab on top of editor). Make sure the code is preserved as is, a one line; it is best to append it to the end of the line where existing Ecwid code ends, without a newline. With this workaround code you will have a correct set of Ecwid widgets and the effects on the Login, Signup, Connect and Search buttons still working.