Hello,
An export of multiple TMs by "Migrating TMs" app failed:

Exporting TM: /NAME1/NAME2
  language direction: de-de=>en-us, TUs: 5092
Export task failed in GS, retrying in 4 minutes...
Export task failed in GS again, skip
ERROR:
System.Exception: Export task failed in GS
   à Kaleidoscope.MigratingTMs.BL.LanguageDirectionWrapperRest.<ExportAsync>d__10.MoveNext()
--- Fin de la trace de la pile à partir de l'emplacement précédent au niveau duquel l'exception a été levée ---
   à System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   à System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   à System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task)
   à Kaleidoscope.MigratingTMs.BL.Exporter.<Export>d__3.MoveNext()

Feedback from Migrating TMs Support : The problem is in GS, sometimes the TM export fails there. Not only through the API (as Migrating TM is using it), but sometimes in the UI as well.
Please check the background job list in GS, and check for the failed TM export task, and contact the SDL support with the specific error messages / error logs.

Failed job GS Log:

Error: System - La référence d'objet n'est pas définie à une instance d'un objet. (details: System.NullReferenceException: La référence d'objet n'est pas définie à une instance d'un objet. à Sdl.LanguagePlatform.TranslationMemoryImpl.TokenSerialization.TokenDeserializer.ReadTagToken(TokenType tokenType, Boolean tokenHasStandardPlacement, Token previousToken, Boolean tokenIsSingleChar) à Sdl.LanguagePlatform.TranslationMemoryImpl.TokenSerialization.TokenDeserializer.Deserialize() à Sdl.LanguagePlatform.TranslationMemoryImpl.TokenSerialization.LoadTokens(Byte[] data, Segment segment) à Sdl.LanguagePlatform.TranslationMemoryImpl.ResourceManager.GetTranslationUnit(TranslationUnit storageTu, FieldDefinitions fields, CultureInfo sourceCulture, CultureInfo targetCulture) à Sdl.LanguagePlatform.TranslationMemoryImpl.TranslationUnitServerFilteringStrategy.Sdl.LanguagePlatform.TranslationMemoryImpl.ITranslationUnitFilteringStrategy.GetTusFiltered(PersistentObjectToken translationMemoryId, RegularIterator iter, FieldDefinitions fieldDefinitions, Boolean includeContextContent, TextContextMatchType textContextMatchType, CultureInfo sourceCulture, CultureInfo targetCulture, Boolean usesIdContextMatch) à Sdl.LanguagePlatform.TranslationMemoryImpl.ResourceManager.GetTranslationUnitsWithContextContent(PersistentObjectToken tmId, RegularIterator iter, TextContextMatchType textContextMatchType, CultureInfo sourceCulture, CultureInfo targetCulture, Boolean usesIdContextMatch) à Sdl.LanguagePlatform.TranslationMemoryImpl.API.GetTranslationUnitsWithContextContent(Container container, PersistentObjectToken tmId, RegularIterator& iter))

In advance, many thanks for troubleshooting help!

Sylvie G.