Critical mod save compatibility issue

Development Modding ARK: Survival Evolved
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I’ve found what appears to be a fairly nasty bug that I imagine is something that will come up a LOT for anyone doing singleplayer mods. Could this be how I did my changes? possibly, but it’s how I got the changes to show up in game after messing around with it almost all day. I imagine this is due to no form of singleplayer ‘save’ system, and how you always load back into the same world on the same survivor, regardless of if you’re playing mods or not. If you load up into a world running a data mod, and then do something along the lines of learning a tweaked engram crafting blueprint, and then go back and try to load into a vanilla map, the game crashes.

My initial modding tweak as just a basic ‘toe in the water’ type experiment, was to try and change the crafting costs for the Thatch Wall. To accomplish this I did the following (only including the workflow that actually succeeded):
Copied EngramEntry_ThatchWall and PrimalItemStructure_ThatchWall into my mod folder, and gave them a unique prefix so that I could find them.
Tweaked some data on the ItemStructure blueprint.
Opened the Engram Entry in my mod folder, and changed it to reference the modded Thatch Wall.
Opened the PrimalGameData_BP in my mod folder, and changed the original Thatch Wall entry in the Master Item List to reference my modded Thatch Wall, and changed the Engram Blueprint Class for the original thatch wall blueprint to match my modded one.
Also have a Remap Resource Components entry set so that the original thatch wall is now referencing to the modded one (not sure if I need that bit, need to test)

Everything ran hunky dory in the editor, saved it, cooked it, put it up on the workshop. Loaded the mod up in singleplayer, my changes worked! hooray! Did some other things, then came back and wanted to look at a bunch of different things in-game so I could work on my master plan, so I loaded into the game with vanilla data. Ran around, punched some trees, pooped on the beach, opened the engram screen and the game cratered on me.

I’m hoping I just did something horribly wrong, but if not, just wanted to let it be known.

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Can you provide an image of the callstack trace messagebox that would have appeared on the screen when the game crashes with that? It’s very likely we can protect against whatever the crash was.

Thanks very much,

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Here’s a screenshot of the error message, not sure why it’s complaining about a coel character though, as I didn’t mess with that.

It’s very easy to generate a crash though, here’s an example of more or less a guaranteed crash for going from modded to vanilla. More or less all you have to do is create an item either via copying or subclassing, REPLACE the original item in the PrimalGameData_BP MasterItemList, play your mod, have an instance of that modded item in the game world (thatch foundation placed on the ground etc), then try to load a vanilla game save. I’ve gotten around that in my own modding efforts so far by only adding items to the MasterList rather than replacing, but that is a very easy thing to break if you don’t know about it.

In my opinion, I think a good fix for this case would be that if someone is trying to run with modded data, that it should create a new SavedArk specific to that mod, so that vanilla only loads vanilla etc. That opens up a whole new can of worms when talking about enabling multiple mods, but that’s another story for another time. :slight_smile: