Invalid instance specialization checksum.

I get the following error when trying to simulate a simulink model-

Error calling generated SFunction, <model_name>_sfun. Invalid instance specialization checksum.

The error is pointing to a statechart within a big model. When the statechart is simulated on its own, there isn't any error.

What does the error message "Invalid instance specialization checksum" mean? Thank you

[Co Melissant]

any ideas on this one? Running ML 2020b we run into the same error