I'm having problems with my Datastore as well. I tried to rebuild my index with vacuum_indexes (didn't know it was a general problem) and got:
Apr 10, 2015 5:17:53 PM com.google.appengine.tools.admin.AbstractServerConnection send1
WARNING: Error posting to URL:
https://appengine.google.com/api/datastore/index/delete?app_id=myid&500 Internal Server Error
<html><head><meta http-equiv="content-type" content="text/html;charset=utf-8"><title>500 Server Error</title></head><body text=#000000 bgcolor=#ffffff><h1>Error: Server Error</h1><h2>The server encountered an error and could not complete your request.<p>Please try again in 30 seconds.</h2><h2></h2></body></html>
This is try #0