by Matteo Scaramuccia.
Hi Martin,
so Master Value is OK while Local Value KO: this explains why you're receiving PHP errors within the local configuration Moodle is running with.
Please, try to set debug to NONE: Do not show any errors or warnings, in Site administration ► Development ► Debugging. This setting will change your Local Value to 0 and will mask all the errors; it will be the setting/value to be used in the production server.
HTH,
Matteo