"When participating in this timestream, your power will be limited to level 10." Indeed, I dropped to level 10.
The first mission is "Get shipping info & clear base" - which shows in the mission list as being at level 12. Meanwhile I'm set at +0. Makes the mission slightly more challenging than expected! I tried leaving the task force and picking up the arc again, resetting notoriety... For some reason the mission is just set to a base level of 12 despite you being power-limited to 10.
After managing to finish the first mission, the other two missions in the arc spawned at the proper level. It's strictly the first one that's incorrect.