[Mobhack]

Just tried the review unit function in an ongoing generated campaign, and all works as expected.

A save of the game in question, and a pointer to whichever unit(s) is/are having a problem would be rather helpful. "Bug" reports without data so the error can be demonstrated, are not that helpful.

My guess is that since it is an ongoing campaign, across different versions then perhaps the original unit was based on something that no longer exists in the latest OOB. Or, it was a home-rolled OOB that is no longer in use having been replaced by a stock OOB, so leaving a blank slot where the original custom unit was. If the review function finds a null unit definition, then it will abort as there is nothing valid there. You can test for that by turning unit IDs on and checking the ID given against the OOB in Mobhack.