i was trying ue5.3 and i used substrate material to create glass as shown in the attached picture and then i made a mirror material but when i placed the object Infront the mirror the glass material didnt show on it as in the attached picture is substrate translucent materials not supported in reflections yet ?
I have also faced problems with substrate 
I suggest you make this post in this topic:
I talked to Sebastian Hillaire aboutt his, substrate PT vs. raster aren’t yet calibrated against eachother, so they won’t have identical behavior. Ideally substrate will enter beta in the near future, hopefully with these problems moreso ironed out.
If you’re using the PT, substrate translucency behavior doesn’t fully match the rasterized view; really no fix until the team updates substrate.
noticed that I noticed that if you install. (Lightning Mode “on”
Surface Forward Shading)
Then, reflections appear for a while. But everything will go bad in a couple of seconds. And the window will switch to the material settings window
