Error importing content/media types with custom tabs - "Set an alias before adding the property group"

[nolmsted]

I'm performing a migration on a v8 site and seeing the following errors when content & media types with custom tabs are being imported after conversion. It appears this only occurs with types that already exist; e.g. updating media types fails but content types will work on an initial import, but fail on subsequent attempts

[[09:43:24 WRN] ContentTypeHandler: Import Failed : System.InvalidOperationException: Set an alias before adding the property group.
   at Umbraco.Cms.Core.Models.PropertyGroupCollection.Add(PropertyGroup item)
   at Umbraco.Cms.Infrastructure.Persistence.Repositories.Implement.ContentTypeCommonRepository.MapGroupsAndProperties(IDictionary`2 contentTypes)
   at Umbraco.Cms.Infrastructure.Persistence.Repositories.Implement.ContentTypeCommonRepository.GetAllTypesInternal()
   at Umbraco.Extensions.AppCacheExtensions.<>c__DisplayClass0_0`1.<GetCacheItem>b__0()
   at Umbraco.Cms.Core.Cache.SafeLazy.<>c__DisplayClass1_0.<GetSafeLazy>b__0()
--- End of stack trace from previous location ---
   at Umbraco.Cms.Core.Cache.ObjectCacheAppCache.Get(String key, Func`1 factory, Nullable`1 timeout, Boolean isSliding, String[] dependentFiles)
   at Umbraco.Cms.Infrastructure.Persistence.Repositories.Implement.ContentTypeRepositoryBase`1.PerformGetAll(Int32[] ids)
   at Umbraco.Cms.Core.Cache.FullDataSetRepositoryCachePolicy`2.GetAllCached(Func`2 performGetAll)
   at Umbraco.Cms.Core.Cache.FullDataSetRepositoryCachePolicy`2.GetAll(TId[] ids, Func`2 performGetAll)
   at Umbraco.Cms.Infrastructure.Persistence.Repositories.Implement.EntityRepositoryBase`2.GetMany(TId[] ids)
   at Umbraco.Cms.Infrastructure.Persistence.Repositories.Implement.ContentTypeRepository.PerformGet(Guid id)
   at Umbraco.Cms.Core.Services.ContentTypeServiceBase`2.Get(Guid id)
   at uSync.Core.Serialization.SyncSerializerRoot`1.FindItem(XElement node)
   at uSync.Core.Serialization.SyncSerializerRoot`1.Deserialize(XElement node, SyncSerializerOptions options)
   at uSync.BackOffice.SyncHandlers.SyncHandlerRoot`2.ImportElement(XElement node, String filename, HandlerSettings settings, uSyncImportOptions options)
[09:43:24 WRN] ContentTypeHandler: Import Failed : System.InvalidOperationException: Set an alias before adding the property group.
   at Umbraco.Cms.Core.Models.PropertyGroupCollection.Add(PropertyGroup item)
   at Umbraco.Cms.Infrastructure.Persistence.Repositories.Implement.ContentTypeCommonRepository.MapGroupsAndProperties(IDictionary`2 contentTypes)
   at Umbraco.Cms.Infrastructure.Persistence.Repositories.Implement.ContentTypeCommonRepository.GetAllTypesInternal()
   at Umbraco.Extensions.AppCacheExtensions.<>c__DisplayClass0_0`1.<GetCacheItem>b__0()
   at Umbraco.Cms.Core.Cache.SafeLazy.<>c__DisplayClass1_0.<GetSafeLazy>b__0()
--- End of stack trace from previous location ---
   at Umbraco.Cms.Core.Cache.ObjectCacheAppCache.Get(String key, Func`1 factory, Nullable`1 timeout, Boolean isSliding, String[] dependentFiles)
   at Umbraco.Cms.Infrastructure.Persistence.Repositories.Implement.ContentTypeRepositoryBase`1.PerformGetAll(Int32[] ids)
   at Umbraco.Cms.Core.Cache.FullDataSetRepositoryCachePolicy`2.GetAllCached(Func`2 performGetAll)
   at Umbraco.Cms.Core.Cache.FullDataSetRepositoryCachePolicy`2.GetAll(TId[] ids, Func`2 performGetAll)
   at Umbraco.Cms.Infrastructure.Persistence.Repositories.Implement.EntityRepositoryBase`2.GetMany(TId[] ids)
   at Umbraco.Cms.Infrastructure.Persistence.Repositories.Implement.ContentTypeRepository.PerformGet(Guid id)
   at Umbraco.Cms.Core.Services.ContentTypeServiceBase`2.Get(Guid id)
   at uSync.Core.Serialization.SyncSerializerRoot`1.FindItem(XElement node)
   at uSync.Core.Serialization.SyncSerializerRoot`1.Deserialize(XElement node, SyncSerializerOptions options)
   at uSync.BackOffice.SyncHandlers.SyncHandlerRoot`2.ImportElement(XElement node, String filename, HandlerSettings settings, uSyncImportOptions options)

Example diff (in this case updating the svg media type)