LooseKeyModifier was causing this for me. Removing it stopped the errors. I think they're meant to be harmless anyway though, and your game should still run fine.. but someone might know better than me.
Edit: I just asked in the Discord about LooseKeyModifier, and was given the advice that the warning messages are safe to ignore, quote: "it's a bug that should be fixed in the next SPT update."
Hope that helps!