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Parker EdelmannParker Edelmann 

Solution for Trailhead error "Your DE Org session has timed out. Please login to your DE Org to continue."

This error can be caused in one of two ways:
  1. ​You've been away for a while and you're now logged out of your DE. This can simply be resolved by logging in again and restoring the connection.
  2. No matter how many times you log out and log in again, having the security setting "Lock sessions to the IP address from which they originated" enabled will prevent you from connecting your Org to Trailhead. For some reason, when trailhead checks challenges, it doesn't use the same IP address throughout the transaction, causing the error because the connector was logged out. As much as I'd like to claim this as my own discovery, @Matt Latto was the one to come up with the solution and posted it on another question, Not able to verify steps of Trailhead project.
Although this isn't officially a question, to my knowledge this information is not anywhere else on the forum, and if it is, it couldn't hurt to post it again.

Thanks for viewing,
Parker
LBKLBK
Hey Parker,
Good point.
And, great that you have decided to post it. Can you please post this content back as an answer and mark it as best answer?
It may help many!