In WindowsPlatformCrashContext.cpp : 304
const FString CrashContextXMLPath = FPaths::Combine( *FPaths::GameLogDir(), *CrashContext.GetUniqueCrashName(), FPlatformCrashContext::CrashContextRuntimeXMLNameW );
CrashContext.SerializeAsXML( *CrashContextXMLPath );
WerReportAddFile( ReportHandle, *CrashContextXMLPath, WerFileTypeOther, WER_FILE_ANONYMOUS_DATA );
When serializing XML file in sandbox he convert path to something different that original CrashContextXMLPath (basically combine path with SandboxPath variable).
But WerReportAddFile doesn’t know about this, resulting missing file in crash report.