The MultiTrans.XliffEditor.log, which is typically located in the C:\ProgramData\Donnelley\Tracing folder shows the following when the logging level is set to Verbose:
 

[Critical] [Xliff Exporter, General] [   1] MultiCorpora.Utilities.CSharp.Common.Exceptions.InvalidSignalException: <g> Nodes NOT Expected while in State XliffExportSegmentState
   at MultiCorpora.Xliff.Importers.Export.StateMachine.Xliff_1_2.States.XliffExportSegmentState.AddTextRunFromGNode()
   at MultiCorpora.Xliff.Importers.Export.StateMachine.Xliff_1_2.States.XliffExportSegmentState.ProcessEndElement(XmlReader reader)
   at MultiCorpora.Xliff.Importers.Export.StateMachine.Xliff_1_2.XliffExportStateMachine.Export(XmlReader reader)
   at MultiCorpora.Xliff.Importers.Export.StateMachine.Xliff_1_2.XliffExportStateMachine.Export(Stream xliffDocument)
   at MultiCorpora.Xliff.Importers.Export.ExportOpenXml.CollectTranslationUnits(Stream xliffStream, XliffStringType exportType, Boolean exportSourceAsTarget, String missingTagMarker, XliffDocumentType type)
   at MultiCorpora.Xliff.Importers.Export.ExportDocx.Export(Stream xliffStream, String exportPath, XliffStringType exportType, Boolean exportSourceAsTarget, String missingTagMarker)
   at MultiCorpora.Xliff.Importers.Export.ExportDocx.ExportXliff(Stream xliffStream, IExportFileDescription exportFileDescription, XliffStringType exportType, String missingTagMarker)
   at MultiCorpora.Xliff.Importers.XEExporter.ExportSingleFile(Stream xliffSingleFileStream, XliffDocument xliffDoc, IExportFileDescription fileDescription, XliffStringType exportType, Boolean forPreview, Boolean validate, IMultitransLanguageList langList, String missingTagMarker)

The XLIFF structure of the document appears to be correct, however, the file was created using an older version of MultiTrans (MultiTrans.Services.Host.Api.exe).  The version used to create the file can be found by using a file editor like Notepad++. Here is an example of what that would like in the file when the version is 7.0.21077.2:
 

<?xml version="1.0" encoding="utf-8"?><xliff version="1.2" mc:creationtool="MultiTrans.Services.Host.Api.exe v.7.0.21077.2"