Jetpack Carousel errors in Dev Mode

Hi Guys,

I’m running Jetpack in Development Mode on the site shown below.

Since updating to Jetpack 6.9 from 6.8.1 the site’s Jetpack Carousel now generates the following error in Chrome Inspector when cycling through images:

“Failed to load resource: the server responded with a status of 400 … yada, yada”

Identical errors now occur on all of my sites set up the same way. I’m aware that Dev Mode has some limited features, but these new errors are a bit alarming.

Any ideas what may be causing them?

Thanks.

https://www.chicoconcours.com/2018/12/winners-2018/

WordPress 5.0.3 with Classic Editor
Self-hosted on WP Engine
PHP 5.6
Jetpack 6.9
Chrome 71 on Mac Yosemite

The page I need help with: [log in to see the link]