Institutions using iBoss as their Content filter, may experience apparently random "missing images" in Quizzes after they upgrade to Gen 4 or 5. This appears to be caused by the new URL format string used by CANVAS for their *.canvas-user-content.com" server. Chrome books appear to be particularly susceptible to this issue.
The "the iBoss cloud proxy limits the URL length and will drop any web page elements that exceed the 255-character limit. " The new *.canvas-user-content.com" server creates URL strings that look like this;