There is a service issue in US East that is impacting some of our worlds. Unfortunately there are global services that route through this region, so the impact is not limited to US East.
We have been informed that the recovery is in progress, and worlds should be normalizing soon.
EDIT: there is impact on expeditions and outpost rush while this issue is still active. Please refrain from attempting to enter either until the issue is fully resolved. We will update this post when that happens.
Thank you for your patience.
EDIT: the service issue is resolved. It is now okay to enter instances such as expeditions and outpost rush.