This could be due to the Shading Mode you have set for this material. It’s currently set to Default Lit and thus requires light to be seen as anything other than black. You may also wish to use the User Interface setting under Material Domain if this material isn’t planned to be used elsewhere. Can you try these and see if they help resolve the problem?
We haven’t heard from you in a while, . Are you still experiencing this issue? If so, have you tried what I mentioned in my previous comment? What were the results? In the meantime, I’ll be marking this issue as resolved for tracking purposes.