Hi,
I have a very simple project that renders lines using the spline mesh component. The line texture however will be rendered using just the lowest level resolution on Play in a viewport window, but will stream mips properly in a standalone window. The blueprint that renders the line only starts rendering on BeginPlay however, so in the viewport there is no rendered instances of that material.
If I drop another static object with the same material in the viewport however, from that point the streaming will be ok.
I can provide the zipped project but I don’t want to publicly attach it.