UE-149717 : I experienced the same error and crash connecting a float4 via a material parameter collection to the emissive input.
Assertion failed: bAllowNonFloat [File:D:\build++UE5\Sync\Engine\Source\Runtime\Engine\Private\Materials\HLSLMaterialDerivativeAutogen.cpp] [Line: 156]
using a component mask with RGB prevented the crash.
