title: SFDC Partner WSDL Login to test.salesforce.com fails seemingly randomly
body: <p>Our Platform is currently integrated to salesforce using the Partner WSDL.</p>
  
  <p>A few days ago we've started getting this error while trying to login into the Sandbox environment:</p>
  
  <pre><code>INVALID_LOGIN: Invalid username, password, security token; or user locked out.
  </code></pre>
  
  <p>Initially we figured one of our API Users was locked out. However, after digging through our logs we noticed that the INVALID_LOGIN failure doesn't happen all the time. It seems to be occurring randomly. Some login attempts are successful. Some fail. What's stranger is that this is occurring across all of our dev servers and even across different client's API Users. However, we're not seeing this behavior on our production instance.</p>
  
  <p>We have multiple development instances of our platform, but only a single production instance of our platform.</p>
  
  <p>I haven't read any documentation that would suggest this, but currently my only guess is that we're seeing some issue with the same API user trying to login at roughly the same time from different dev instances causing the issue. Is that possible or could this be caused by a completely different issue I'm unaware of? I'm far from an SFDC expert. Is there some more useful debugging information I can get from SFDC?</p>
  
  <p>I don't think this information would be that helpful, but in case there is some edge case I'm unaware of our platform is written using .NET / C#.</p>
  
  <p><strong>UPDATE:</strong> These login errors seemed to have stopped in the past 24 hours. No code / process change on our side. It would be nice to understand what the cause of this was. If anyone has insight on it.</p>