UHT is expecting some method that should be defined during code generation. My guess is that since you’re providing a CustomThunk that it’s skipping that portion of the generation and the code you copied is likely out of date with what UHT expects.
Honestly, looking at the code, I don’t see any reason why this needs a CustomThunk. It looks like the original author was using it to call that Generic_GetDataTableRowByIndexWildCard method, but you could easily wrap that in a namespace or just keep it as a static method in the CPP and have all your blueprint function libs call into that.