Well, you also have the case of very competent engineers underperforming due to stuff happening outside home. Martial problems, family problems, health problem

Well, you also have the case of very competent engineers underperforming due to stuff happening outside home. Martial problems, family problems, health problems, depression, addiction, and what not. Not saying that two months is enough to resolve those problems, but if for whatever reason such engineers are able to finally block those stressors, and bring their A-game to "beat" the PIP, then that should absolutely be a good reason to keep them aboard. A PIP should not be a delayed 2-month firing process. It should be a legitimate chance for someone to improve.