Under Clients > [choose group] > Policies tab. Under Location-specific Policies and Settings, click on the plus sign in front of Location-specific Settings. Next to Client User Interface Control Settings, click Tasks > Edit settings. (If policy inheritance is turned on, you must either turn it off, or modify the top group, usually My Company.) See attached image.
If you set this to Client control, or to Mixed control (ensuring Client Logging Options is set to Client), you should be able to clear the logs on the client.
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