I'm having the same problem on XB1X except I'm at 36. I haven't finished the last episode of the
main story, but I have finished Peril on Gorgon and I'm almost done with Murder on Eridanos.
My Current XP and XP needed to level are both at 480,000. I planned to finish the main story
after the DLCs. Maybe the next time I'll finish the main first.