On my D8.3 site I have a content type with an image field. If I upload an image, it sits outside the content, where colorbox will work. If I use the Insert module, the image is easily inserted into the content area but now Colorbox does not work. I had identical problem with D7 but was able to workaround by using Panels to create a page where images were in a sidebar with the content.
I would like for all images in content to work with the Colorbox module.