I just upgraded Lightroom to CC from 5.5, and all my web gallery definitions have gone. I use a custom template for my galleries, which I've copied into the webengines folder, however any collections I select revert to the default 3x3 grid with basic settings.
Are the definitions stored somewhere I could copy from, or will I have to recreate them?
Were they were Flash galleries? LR CC no longer supports Flash, which may be why you aren't seeing them: Lightroom 6 dropped Flash web pages, HTML5 galleries poor solution as best | Photoshop Family Customer Community