We've bumped into this issue too, but it was through the MoreLikeThis query parser. Internally it uses the get handler to obtain the seed document. One of our SOLR collections uses a shard router that is not the document id. The get handler will fail if the value of the document id is not the same as the routing key. And then this causes the CloudMLTQParser to issue the message "Error completing MLT request. Could not fetch document with id [/x/]"
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