These are the steps I use if an image isn't showing up and sometimes it resolves the issue with the video:
Option 1. Reload the page
If a simple reload of the page does not appear to be fixing the issue (control-R or command-R on macs), try control-shift-R (or command-shift-R on macs) to reload the page and force everything to re-download. Your browser keeps a cache (store) of images and files it has downloaded before. Control-shift-R should tell the browser to re-download everything.
That usually fixes the issue for me, but if things are still not working and you don't think it is poor network connectivity, there are some "stronger" options below that you can try.
Option 2. Empty cache and hard reload
Sometimes it is necessary to empty that cache first to force all images or other files to be downloaded again.
In chrome, you can hit control-shift-i (or command-shift-i on macs) to open the developer console panel. on the right. Then right-click (or control-click on macs) on the reload button and select Empty Cache and Hard Reload, as pictured below. Hit control-shift-i again to close the developer tools pane.

Option 3. Clear browser data
In Chrome, you can clear all the images and files stored by your browser. Click the 3 vertical dots on the top right of Chrome, go to Settings, and scroll to the bottom and click on Advanced. Click on Clear Browsing Data. You can also get there directly by going to this URL: chrome://settings/clearBrowserData

Clear recent images and files from your browser like so:

Reload the Canvas page to see if that fixes the issue.
See this Clear browsing data page for more details.
Option 4. Clear Chrome browser extension
Another option is to install the Clear Chrome. browser extension for Chrome. It adds a button in the toolbar that will clear your cache any time you press the button (and optionally it will reload the page for you, too).