I see you're using a cache plugin which supports object cache. The error comes from that part (file wp-content/object-cache.php). Can you please check that? Maybe try another cache plugin, or update it to the latest version.
FYI: Meta Box uses WordPress function wp_cache_get_last_changed, and this function calls object cache.
I see. That's a way to use Redis (object cache) to cache the whole page. Can you try deactivate the plugin to see if the problem still occurs. And also check your disk/ram space. Maybe Redis uses too much space, which cause the data broken, and can't be unserialized.
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