The marker is on the pcell subMaster (i.e. the variant), which will only be created by instantiation. Given that the failure may only arise when particular combinations of parameter values are given, it really only makes sense to be produced by virtue of instantiation.
You don't have to check the log file; you could check the instId~>master and check for any markers. I can't remember whether these end up as marker objects in IC61X, or whether they are still shapes on the marker/error layer purpose pair - either way they are pretty easy to detect programmatically.