A cautious hypothesis for the Ninth Legion's disappearance

What may have happened to Legio IX Hispana, the Ninth Legion?

A depleted British force may have suffered a disastrous northern action and been replaced rather than reconstituted.

The Ninth Legion's fate remains an open question rather than a solved mystery. One hypothesis is that detachments had already reduced the force available at its British base when raiders struck from the north. A pursuit into difficult Scottish terrain could then have surrounded and destroyed much of the remaining infantry, perhaps with the eagle or commander lost. Enough survivors may have returned to prevent the event from resembling the total destruction in the Teutoburg Forest, but the unit could still have been too damaged or disgraced to rebuild.