I use Yoast Video SEO on my wordpress site and I routinely get an error in Google Webmaster Tools telling me there's an error in my sitemap.
I worked with tech support and came up with the following workaround. The problem is that the problem keeps coming back. Each new video I post needs to go through this workaround to post the correct date.
Here's the fix:
Cut the video from your post or page.
Update / Save the page (without the video)
Paste the video back into your post or page.
Update / Save the page (with the video back in.)
Then Re-Index videos in the Yoast Video Plugin and go back to Google Search Console (formerly Webmaster Tools) and resubmit the sitemap.