Yes I had this doubt only. I have faced similar issue with my local AEM
instance and suddenly none of query like JCR-SQL2, xpath , query builder
were giving any result.That time I realized something went wrong with my
local AEM instance. Please try to search that user using useradmin
console as shown below - One more request , just try to execute any
other query in CRXDE, query builder and see whether it gives you result
or not.