In the #Recursion anomaly, following each weekend event there is a period of time in which artifacts can be moved around, as summarized on the Ingress Report EP46 (transcript)
I've also heard that there are rules around the minimum level of a portal that holds an artifact.
What is the full set of rules, or at least sitreps for the various artifact movements to date (like FRANCE SITREP FOR ARTIFACTS 7 AND 8 #Recursion Shards, we deliver. Ingress Resistance Paris - France - Google+)
Update: more questions:
Do artifacts only move at the top of the hour or 30 minutes after the hour?
If there are multiple eligible links out from a portal that has an artifact, where does it move to?
What does "locking" of artifacts mean?