We recommend using the latest version of Google Chrome web browser to resolve a Canvas Dashboard not loading class cards or global navigation menu button icons.
To Check Your Version of Chrome (On PC, Mac)
STEP 1
On your computer, open Chrome
STEP 2
At the top right corner, look at More 
STEP 3
Click Help > About Chrome

Chrome will check for updates and let you know if you're up-to date.

If you are using a Chromebook/Chrome OS, please contact your manufacturer's website for instructions and support in updating Chrome.