Okay. Knowing all that. A possible reason (Seen on Airbus a few times) was a grossly incorrect waypoint wind entry. Maybe for the waypoint immediatly proceeding or following where you're at "now", the wind was entered with a gross error ( or TROP altitude entry error). In the Airbus, that will effect max levels to some extent, often to a large extent.
Sorry, but my Boeing knowledge is really rusty. Otheriwse, just trying to share some ideas about it.