For those unfamiliar with the service, Shadow allows subscribers to play triple-A titles on their smartphones, tablets, set-top boxes and computers, while high-end remote servers take the burden of processing the graphically intensive games.
The French company that runs the service confirmed via a Reddit post that Apple has removed its streaming apps for iOS and Apple TV from the App Store for a "failure to act in accordance with a specific part of the Apple App Store Guidelines." The Shadow app for Macs was unaffected by the other apps' removal and remains available on the Shadow website.
In the announcement, the company said it was "currently investigating the situation" and would be working on a plan to bring Shadow back to Apple device users as soon as possible.
It's unclear what aspect of Apple's App Store policy the service has contravened, but the situation sounds similar to when Apple rejected Valve's Steam Link app in May 2018 due to App Store review guideline violations related to in-app purchases.
Valve's app eventually returned to the App Store a later, but only after it removed the option to purchase games from within the app.