@Sonic is right, I encountered this before: What's the Codegolf_Temp database (and why does it mess up my query)?. That was a real bug; the SEDE refresh was stuck that Sunday and it took a staff member to repair the situation.
This time it's running smoothly; @rene explains here that it's part of the regular import process. You can check this simple query or a more complex one by @rene (fill a random number for the seed/cache breaker parameters) how the import is progressing; as I'm writing this, those _Temp databases don't exist anymore but Stack Overflow is still being imported.
You can either
- wait until the import is finished; I've set up a weekly monitor on a related query, and last week the import finished at 10:20 UTC.
- adjust the query so that it ignores _Temp databases. That is relatively easy (again, @rene explains how to do this), but the downside is that results are partially stale.