The target location specified by path segment 'Abbreviation' was not found.

I think I got this exception, because my app was not up to date. I believe it's essentially the "Opaque change" scenario except for a known type, but unknown property, so needs some sort of special handling (e.g. model versioning?)

Error: SystemTextJsonPatch.Exceptions.JsonPatchException: The target location specified by path segment 'Abbreviation' was not found.

at SystemTextJsonPatch.Exceptions.ExceptionHelper.ThrowJsonPatchException(JsonPatchError jsonPatchError)
   at SystemTextJsonPatch.Internal.ErrorReporter.<>c.<.cctor>b__2_0(JsonPatchError error)
   at SystemTextJsonPatch.Adapters.ObjectAdapter.Add(String path, Object value, Object objectToApplyTo, Operation operation)
   at SystemTextJsonPatch.Operations.Operation`1.Apply(TModel objectToApplyTo, IObjectAdapter adapter)
   at LcmCrdt.Changes.JsonPatchChange`1.ApplyChange(T entity, IChangeContext context)
   at SIL.Harmony.Changes.Change`1.ApplyChange(IObjectBase entity, IChangeContext context)
   at SIL.Harmony.SnapshotWorker.ApplyCommitChanges(SortedSet`1 commits)
   at SIL.Harmony.SnapshotWorker.UpdateSnapshots(SortedSet`1 commits)
   at SIL.Harmony.DataModel.UpdateSnapshots(CrdtRepository repo, SortedSet`1 commitsToApply)
   at SIL.Harmony.DataModel.SIL.Harmony.ISyncable.AddRangeFromSync(IEnumerable`1 commits)
   at SIL.Harmony.DataModel.SIL.Harmony.ISyncable.AddRangeFromSync(IEnumerable`1 commits)
   at SIL.Harmony.DataModel.SIL.Harmony.ISyncable.AddRangeFromSync(IEnumerable`1 commits)
   at SIL.Harmony.SyncHelper.SyncWith(ISyncable localModel, ISyncable remoteModel, JsonSerializerOptions serializerOptions)
   at SIL.Harmony.DataModel.SyncWith(ISyncable remoteModel)
   at FwLiteShared.Sync.SyncService.ExecuteSync(Boolean skipNotifications)
   at FwLiteShared.Projects.CombinedProjectsService.<>c.<<DownloadProject>b__16_1>d.MoveNext()
--- End of stack trace from previous location ---
   at LcmCrdt.CrdtProjectsService.CreateProject(CreateProjectRequest request)
   at LcmCrdt.CrdtProjectsService.CreateProject(CreateProjectRequest request)
   at LcmCrdt.CrdtProjectsService.CreateProject(CreateProjectRequest request)
   at LcmCrdt.CrdtProjectsService.CreateProject(CreateProjectRequest request)
   at FwLiteShared.Projects.CombinedProjectsService.<>c__DisplayClass16_0.<<DownloadProject>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at FwLiteShared.Projects.CombinedProjectsService.DownloadProject(ProjectModel project)
   at FwLiteShared.Projects.CombinedProjectsService.DownloadProjectByCode(String code, LexboxServer server, Nullable`1 userRole)

Start at LcmCrdt.Changes.JsonPatchChange.ApplyChange and follow the sync path through SnapshotWorker.ApplyCommitChanges and SyncHelper.SyncWith. Reproduce the project download or sync failure, then determine the expected handling for a patch targeting a known type with an unknown property; done means this case no longer throws unexpectedly.