Earlier today it was discovered that trying to upgrade Urbit OS on a ship that was multiple versions behind would fail. The issue was identified to be broken state migration functions in Ames. Thanks to ~norsyr-torryn for helping me figure this one out.
A fix for the problem has been pushed out and is propagating across the network.
%base hash (check with +vat %base): 0vg.kniql.spcko.ms91o.v2qng.8ah7k.evj1b.sbcko.3deer.3f5eq.fk0pn