This was the cause: Assertion failed: NumPlanes <= 12 [File:D:\build\++UE5\Sync\Engine\Source\Runtime\Renderer\Private\DistanceFieldShadowing.cpp] [Line: 583] - #6 by erduagile
Either ‘Get Viewport Size’ function returned 0x0 for the 1st tick on PIE. A simple ‘greater than’ and a branch solved it!
Still a bit puzzled as to why the Desmos graph doesn’t work tho…