I played Krastorio2 with my grandson in multiplayer, and we decided to try it first in sandbox mode with all recipes unlocked. Shortly after he joins my hosted game he is getting thrown out.

Main error message is:
4.029 Script @Krastorio2/lib/private/data-stages/utils/log.lua:110: Message: 'This recipes are not unlockable, maybe is an error: { "uranium-rounds-magazine", "nuclear-fuel", "imersite-rounds-magazine" } [from findNotUnlockableRecipes()]'

So it seems the default_locked_vanilla_recipes in line 1915 of lib\private\data-stages\recipes.lua needs to be appended with "uranium-rounds-magazine", "nuclear-fuel", "imersite-rounds-magazine".

Could you please post the entire contents of the crash? Or perhaps the log file?

Sure. Here you go.

https://forums.factorio.com/viewtopic.php?p=535162#p535162

Oh... reading the log file again, the Krastorio message seems to be a red herring and it is a crash of the main game. Perhaps you can confirm and I'll post it in the right place.

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Yep. Congratulations, you found a base game crash!

Problem was due to a corrupted installation. Thread can be deleted or closed. Krastorio2 is great!