Understanding Firebase App Check rejection

Question

My project use Firebase App check on iOS using DeviceCheck & App Test, cloud functions have enforcement checking wether auth context.app is undefined or not, simply like:

if (appCheckEnabled == true && appCheckFunctions[functionName] == true) {
    if (context.app == undefined) {
        appCheckFailure["reason"] = "context is undefined"
        appCheckResult["valid"] = false 
    }
}

Everything work fine on my devices and my team's device and most of users are fine too. Problem is that i have some users that are rejected on iOS, we try to understand why as we asked us if the app is downloaded via the app store and correct link, we also ask a video of the device and thing is everything looks fine (also check for jailbreak). So i have a few question about app check :

• As App check is in beta is it possible to get some false positive result ?
• What can be the reason on iOS for the context.app of the cloud function to be undefined ?
• Is it possible they get rejected because of the quotas ? I could not find any ways to check if the Apple Device Check quotas have been reached ? Anyone know where i could find stats about it ?

Thank you for any answer that could help understand.