There's these huge broken white boxes, instead of a line divider. 

It's fine on Chromium browsers, but why is this happening on Safari? I do not want to switch browsers all the time, as Safari is my main browser. All extensions are turned off and history/cache cleared, prior to taking this screenshot.

Cross-tracking prevention is turned off (unchecked).

This is NOT present when I use the Canvas Student app on iPadOS or iOS.