Did you manage to solve it?
Having the same issue.
Also your plugin is not working in 4.23.1 and it is not rebuilding with following errors:
SkeletalMeshMergerBPLibrary.h(58) LogCompile: Error: An explicit Category specifier is required for any property exposed to the editor or Blueprints in an Engine module.
SkeletalMeshMergerBPLibrary.h(61) : LogCompile: Error: An explicit Category specifier is required for any property exposed to the editor or Blueprints in an Engine module.
SkeletalMeshMerger/Public/SkeletalMeshMergerBPLibrary.h(64) : LogCompile: Error: An explicit Category specifier is required for any property exposed to the editor or Blueprints in an Engine module.
SkeletalMeshMergerBPLibrary.h(67) : LogCompile: Error: An explicit Category specifier is required for any property exposed to the editor or Blueprints in an Engine module.
SkeletalMeshMergerBPLibrary.h(70) : LogCompile: Error: An explicit Category specifier is required for any property exposed to the editor or Blueprints in an Engine module.
SkeletalMeshMergerBPLibrary.h(74) : LogCompile: Error: An explicit Category specifier is required for any property exposed to the editor or Blueprints in an Engine module.
SkeletalMeshMergerBPLibrary.h(78) : LogCompile: Error: An explicit Category specifier is required for any property exposed to the editor or Blueprints in an Engine module.