Crash when open level

When I try to open the second level of my game, it crashes on packed game. It works fine when playing in editor.

The log file has this error:

[2017.03.16-00.32.08:509][321]LogWindows:Error: Assertion failed: LocalExportIndex.IsNull() [File:D:\Build++UE4+Release-4.15+Compile\Sync\Engine\Source\Runtime\CoreUObject\Private\Serialization\AsyncLoading.cpp] [Line: 1915]

Opening the file AsyncLoading at line 1915, the assert has this comment: “otherwise we have two exports that match and our criteria is not good enough”. I have no idea what it means, but perhaps someone can explain it to me?