Kaltura incompatibility with Sprint ISP

I’m an end user with only a bit of technical expertise but I thought I’d run this past the experts.

I’m told that the videos which stream at americastestkitchen.com, cookscountry.com and cooksillustrated.com are Kaltura.

I’ve been having a hell of a time playing these videos through the website-- with a few outlying exceptions, generally when I click on the video to initiate playback, I get a white or beige box.

I finally isolated the behavior to my ISP. I have an unlimited mobile data plan, so I use my Sprint 4G phone as a wireless hotspot. I found that when I use my company’s VPN, the videos consistently play. When I turn it off, they don’t.

I’d be curious to know if anyone here with a Sprint phone can recreate the problem, and if this is a known issue with Sprint, or with Kaltura’s format?