I'm not sure why the GUI for FMRS doesn't show up. Please help.
In a small demo scenario, I have two stages, one with a command pod and the other with a probe. No window automatically appears on screen and no mod tab for FMRS is visible in the sidebar. You can view the other screenshot to see what mods I have installed.
I'm running 1.12.5 and manually unzipped the FMRS folder into GameData, from the latest release (1.2.9.5) of the mod.