Thanks for the additional info.
I was wondering about the specific error to get an idea of what kind of error was occurring as that may be relevant to how the problem occurred. I was puzzled at how the case convert could be erroring, but I understand now that in the situation where it failed, it was that in effect the case converter becoming “misconfigured” because of the change in the data. That may turn out to be relevant, and useful for tracking down the scenario if something similar occurs again.
I agree that this would hamper debugging, but whilst created and used many components, any failures within the components have never caused me this problem, so I’d also be quite keen to understand it, if it happens again.
As an aside, I had a strange (different) issue with components a while back where certain components, if placed on an inactive branch would cause it to be reactivated, and thus cause the workflow to fail, but it didn’t happen for all components. It took over a year to finally find a pattern to it, (and the fix for that obscure error is coming in KNIME 5.3 
)