include in remote.php ends up in error 500 accessing CardDAV contents

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OC 6.0.4
Thunderbird 24.6.0
SoGo Connector 24.0.5/24.0.4/24.0.2 (tried with these versions)
It takes some days to discover my adressbook is not synced anymore (without error messages) and hours to find out it has to do with adding the line "require_once 'apps/superlog/spy.php';" in my remote.php. This works well for WebUI and Client activities, also CalDAV. But the SoGo Connector (AddOn for syncing CardDAV with TB addressbooks) fails with error 500 for every vcf just after correctly compared the ctag!?
Commented out the line -> the sync worked immediately. Can't debug this further on the OC side - sorry. Thanks for Help - superlog is a perfect solution.