I’ve checked in a fix for 4.13 (CL# 3046429 in Dev-Framework, will make it to UE4 main in a week or so). The issue is that the tile map components could read the default tangent basis before it was initialized (only ones created before any sprite or tile map has been rendered once), which is why 4dzirt’s workaround fixes things, as it will cause the render state to get recreated and regenerate the vertex buffer.
When testing this I also found an issue with lit grouped sprites, and fixed that as well, CL# 3046428.
Cheers,
Michael Noland