After rB3b6ee8cee708 by @HooglyBoogly vertex groups were moved to mesh data, and versioning code was provided to upgrade old files. However, it fails to consider the case of linked duplicates having different name lists, and dependent on the object order can cause some of the names to be lost. This can even be all of them, if there is a duplicate without any names, which can be easily created by lazy Python code. To fix this, change the code to use the longest available name list. Differential Revision: https://developer.blender.org/D11958