In development mode (< script src="https://www.gstatic.com/amphtml/v0.js" development >< /script >) the console says that my lightbox is missing this attributes : from,width,height.
The first is undocumented and the lightbox works fine even without it
Width and Height are totally ignored even if setted

< amp-lightbox id="mainLightbox3" class="lightbox1" layout="nodisplay" >
.....
< /amp-lightbox >