Two players contacted me that vassal no longer run on recently updated machines with Mac OS 10.12 Sierra and the latest Java 8 update 151. I have updated; actually my primary Macbook is limited to 10.7 (Lion), cannot tell what java is used. Other uses 10.11.8 El Capitan with Java 8 update 91. Both run vassal fine.
One used a recent time machine to go back to 10.11.8 with Java 8 update 91. The other took his machine to an Apple store, had it wiped, 10.12 reinstalled but installed Java 8 update 91. Vassal back to running in both cases.