I have seen management target older, higher paid employees and they go from exceeds on performance to partially meets. There is no recourse with HR as they work for management. They also then reduce an equal number of younger people to offset the older ones. Rinse and repeat.
This is GM's modus operandi. It should be illegal but they found a loophole and now they're doing whatever they want. This is costing us some amazing and very much needed employees with loads of institutional knowledge, but nobody in the management cares.