What can trigger "App uses the itms-services URL scheme to install an app" rejection?

I'm an indie developer. My latest minor update for my game which has been on the Mac App Store for 13 years and which has spent time at #1 on the download charts just started getting rejected for the following reason:

Guideline 2.5.2 - Performance - Software Requirements

The app installed or launched executable code. Specifically, the app uses the itms-services URL scheme to install an app.

However my app is certainly not installing any apps and to the best of my knowlege it is not using any itms/itunes/etc. type URLs in any way, so I can't figure out what would be triggering this claim. Inquiries as to what app I am supposedly installing or what URL I am supposedly using have yielded 'no further information can be provided'.

Has anyone run into something similar? Any ideas on obscure scenarios that could trigger this particular rejection? Or any advice on what one should do in my situation? I feel a bit stuck. Has anyone had luck with the appeal process for this sort of thing (to at least get more information)?

What can trigger "App uses the itms-services URL scheme to install an app" rejection?
 
 
Q