SERVER-41327 reported a query failure with CursorKilled error along with the following error in acquiring the lock for storage stats collection:

"Timed out obtaining lock while trying to gather storage statistics for a slow operation."

Though the above message is just a warning, it sounds like this is the cause of the query being killed. Improve the error to remove this confusion and to notify that at worst this would result in the absence of storage statistics from slow operation logs.