We recently updated to WebAPI v2.13.0 and Atlas v2.13.0-DEV ; and recently fixed a problem with Cohort Definitions > choose existing definition > Export > SQL by using v2.13.0-issue-2876 .
Now we are getting ‘invalid search’ in Atlas.
It seems that this problem went away after a bit. 
You had a 404 and a 401. This looks like you had a permissions error that may have been changed on the server side, or even in the file system. Log this with your helpdesk, there are so many things that could have caused this.