Cloudant: couch returned 500

Question

Getting cloudant error on find query:

{
   "selector": {
      "isValid": {
         "$eq": true
      }
   }
}

Could not find document query: "{exit,lru} couch returned 500"
Could not find document query: "{exit,noproc} couch returned 500"

Trying to execute simple find query and getting this error. The expected result should be returned result of the query.