Assertion failed: MaxSubjectZ > MinSubjectZ

When importing landscapes from World Machine (R16 file) I sometimes get an error that makes my sub-level maps unopenable with the editor crashing with “Assertion failed: MaxSubjectZ > MinSubjectZ”

This is happening on otherwise blank maps, however it is inconsistent in that it doesn’t happen to all the maps.

Assertion failed: MaxSubjectZ > MinSubjectZ [File:D:\Build\++UE4+Release-4.17+Compile\Sync\Engine\Source\Runtime\Renderer\Private\ShadowSetup.cpp] [Line: 728] MaxSubjectZ -nan(ind) MinSubjectZ -1048576.000000 SubjectBounds.SphereRadius 0.000000

UE4Editor_Core!FDebug::AssertFailed() [d:\build++ue4+release-4.17+compile\sync\engine\source\runtime\core\private\misc\assertionmacros.cpp:349]

If you want I can post the rest of the stack trace. Have already sent the error reports to Epic.
My only solution so far has been to delete the UE4 map asset & reimport the R16 landscape file.
I have not experienced similar behavior in 4.16, though might’ve just gotten lucky.

Cheers,
Dave

Seems to happen when I add a directional light to the sub-level, open another level and try & open the sub-level “later”. It’s not clear what triggers the exception, as “later” seems to be random.

WORKAROUND: add the sub-level to another level using the Levels panel, remove the directional light, save the both maps, remove the sub-level from the main level and it’s fixed.

Still, there’s a bug somewhere.

This keeps happening more frequently and is really irritating.

Epic let me know if you need any additional info, would be happy to help.

Works fine in 4.18.