Not sure if this has been discussed or not...
After getting the relic (either from Mars or Venus), once you pass the portal sometimes it doesn't teleport you back on the Atheon stage but rather passing through the same portal either from Mars or Venus.
Why is that?
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It's a glitch, minir inconvenience, once you notice you're not at Atheon walk through again... It's a bug and Bungie is aware of it, not sure if they are working on a fix and if so then don't know how soon