In the history of miserable, shitful reasons for things not working… this has to go into the top 100.
The dedicated server command line has to include the map name NOT the mod name in the launch line. Map name… as in your_map_name.umap.
WRONG: ShooterGameServer.exe /Game/Mods/[mod_id]/[mod name]?listen?ModId=[mod_id]?etc. etc.
RIGHT: ShooterGameServer.exe /Game/Mods/[mod_id]/[map name]?listen?ModId=[mod_id]?etc. etc.
In my case, my cooked map was Storm.umap… so when I tried to use ShooterGameServer.exe /Game/Mods/481947269/Ultra-Realism?listen?ModId=481947269 when I should have used Storm