iPhone 7: OTA Distribution not working (on other iOS 10 Devices, there is no Problem)

Hi at all!

We have massive problems to install our company employee app via enterprise distribution on iPhone 7. Other iOS 10 devices make no problems. Has anyone a guess?

We are using a website for distributing the apps to our employees:

itms-services://?action=download-manifest&url=https://urlpath/appname.plist

The https-certificate is a trusted certificate. The installation site and the app-manifest has unlimited accessible via internet. Only the ipa-File has limited access via basic authentication:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>items</key>
    <array>
        <dict>
            <key>assets</key>
            <array>
                <dict>
                    <key>kind</key>
                    <string>software-package</string>
                    <key>url</key>
                    <string>https://urlpath/access_limited/appname.ipa</string>
                </dict>
                <dict>
                    <key>kind</key>
                    <string>display-image</string>
                    <key>url</key>
                    <string>https://urlpath/appicon_small.png</string>
                </dict>
                <dict>
                    <key>kind</key>
                    <string>full-size-image</string>
                    <key>url</key>
                    <string>https://urlpath/appicon.png</string>
                </dict>
            </array>
            <key>metadata</key>
            <dict>
                <key>bundle-identifier</key>
                <string>com.mycomp.appname</string>
                <key>bundle-version</key>
                <string>1.97</string>
                <key>kind</key>
                <string>software</string>
                <key>title</key>
                <string>App Name</string>
            </dict>
        </dict>
    </array>
</dict>
</plist>

Bye,

Andreas