Well, you’re not using the Cesium JS API directly, so what is this? Some XML wrapper? That Angular wrapper?
The problem could be anywhere between what you’re using and the API, but I’d probably start with making sure my ‘positions’ is correct (in the code put a console.log(positions) and check your log), then move through the stack in search of answers. There’s really no way for us to know what you’re doing here, and you’re also not explaining what “the complete point or polyline” means, what’s expected and what you’re getting.
This … doesn’t really explain what the problem is. I also think you need to start answering the other questions I had, the XML or templating language is not part of Cesium JS. I understand that speaking English might not be your forte (I know, English is my 4th language, it can be tricky), but it’s hard to know how to help you otherwise?