The windows of results is always truncated, it stop at the begin of main body. This way the search results are never visible. The module should have a big zindex and go over the mainbody. If you want to try, you can try to search with the term Fusolab. Other search modules (you can try the one just above) instead show the results correctly by going over the main body.
This is not a problem with the z-index.
It's a problem with the template module position, hiding the overflow.
Add this css in your template:
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