Objects missing from published prototype

I'm working on a project that has iphone, ipad and web artboards. Everything has worked fine until now. One of the iphone footers has objects that doesn't show in the published prototype at all. I've made a symbol from the footer and the other footers (exactly same ones) are showing correctly. I've tried ungrouping or updating the symbol, duplicating the artboard and deleting the old one -everything! Few logos and one button just doesn't show when I'm viewing it in browser. Other changes in the same artboard updates correctly and the whole thing looks fine when exported to zeplin. Any ideas what might cause this?