I don’t know if this has already been mentioned here:

In previous versions of Web Designer Premium, when an element was hidden (made invisible) in the Page & Layer Gallery, it was for purposes of preview and export not there. It was a convenient way to compare previews with and without a given element. (The main exception, of course, was when an entire layer was hidden: it appeared on export.)

In version 17 (I didn’t check v16), the element is hidden from the design project only. When the project is previewed or exported, the hidden element appears as a normal element. The only way to “hide” it is to delete it. That is not only risky, given that one must remember to undelete it afterwards, but it is problematic, in that if one wants to hide several elements and then pick and choose which to keep, it is a nightmare of deleting and undeleting back and forth.

Please fix the problem and make hidden elements invisible in export and preview once again. Thanks.