I recently noted that the new preview engine of Dreamweaver CC 2017 has a real hard time previewing correctly <canvas> contents that involve JS and vector coordinates. This both applies to live preview and also F12 (Preview in browser).
For the moment, I needed to revert to the latest CC 2015 version.
I leave this note for future troubleshooting and development.
Did you File a bug report along with related files so the engineers can try and replicate the issue at their end?
In DW Help > Submit Bug/Feature Request.
This forum is mainly product users like you.
I can't give files since I realized this while correcting some student works.
(I would need their authorization to submit their work).
All worked fine directly in the major browsers. The JS code, the body's init() function call and the canvas tag were all well coded.
The issues were truly linked to the interpretation made by the new preview engine.
I needed to say to the students "The browers always tell the truth" since I was sharing with Connect.