This is only a WARN and not showing any impact. Still like to know what is going on and how to fix this.
First, this is not a bug. Warning messages happening when EM gets shut down with a kill signal or crashes has a good chance of seeing issues with the traces. And this seems to be an issue with the traces index directory
If the EM crashes after 'Error querying for correlated traces' is repeatedly displayed. Then, it is the timing when the index of the trace file is damaged and can not be accessed, but the specific timing is not known.
It can't reload older transactions either in the "traces" tab in Investigator, or by the Historical Event Viewer. At that time, the trace file is corrupted or just before destruction, but the EM does not crash and the following message appears in the log file.