Been having this error, it may not be related to vanish as my game just closes and this error appears in the log.
Only happened after the Halloween update so may well be rust itself.

12.345.678.90:12345/76561############/nnnnnnnnn kicked: Steam: InvalidAuthSession
NullReferenceException: Object reference not set to an instance of an object
at Oxide.Plugins.Vanish+VanishPositionUpdate.OnDestroy () [0x00022] in <ccc1f0561e2a42fea0703685ba7118f6>:0