We also have an instructor that has reported this problem. On Oct 9th, she ran the link validator and came up with 300+ errors, mostly YouTube videos.
I did some testing and found that all of the videos that failed were YouTube videos that she added by copying the video's URL and pasting it into a page in Canvas. When YouTube videos were added by using the embed code from YouTube or the YouTube button in the RCE, they didn't fail. Since I didn't find any mention of this problem in the Canvas forums and no mention of an update to the Link Validator in the Release Notes, I told her that maybe it was a change on YouTube's end that caused the problem.
The curious thing we then realized is that it is an intermittent problem. She re-ran the validator on 11/3 and received only 60 errors, but the ran it again on 11/5 and again received 300+ errors.
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