This also happens to me.  There is a link validator that I run to find these issues before students see them.  You can find it in course settings, at the bottom of the right-side menu. 

As for avoiding broken links, I have found that links are more stable when I create them using the automatic buttons within canvas.  So, for example, highlight the text, click files in the right-side menu and select the file from the list, rather than copying the web address of the file and inserting the link through the RCE.  

I had also previously found that links I associate with images to create a button almost always fail, either because the link is broken, or because the embedded image is linked to the previous course, which students do not have access to.  I have been assured that the new RCE does not have that problem.

Regardless, there are a few links I seem to have to recreate every semester.  Overtime, I have replaced as many as possible with text instructions for how students should navigate to the item, instead of a link.  Fortunately, for those links that I have to keep, despite the fact they keep breaking, the link validator tool manages to find them all.