Translucent materials do not appear in Lumen as of today (with Substrateor not). This is the current state. Please report lumen issues in the Lumen thread.
If I understood correctly, those issues are from a project with Substrate OFF. Please remember that this is a thread for Substrate only. See my comment from Substrate - Feedback Thread - #194 by SebHillaire
If I missunderstood 
and it is with Substrate, then remember that the path tracer is not up to date with Substrate.