Nonce verification failed – comment error

People who want to comment on my blog recently get a lot of Nonce verification failed messages. I can’t remember if that started since the latest update of the plugin WP fc. I asked what might be the reason in the WordPress support forum, and deactivating the plugin WP fasted cache was suggested to find out if that might be the reason. I tried this, and test comments went through without a problem. But I would rather find out which setting might cause the problem and keep it activated. Any suggestions if the plugin might cause this? I have the plugin deactivated at the moment.

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