> suss out the root cause (usually easy) and eliminate it (usually hard).
Well in this case it maybe what happened. They are eliminating the root cause -- the actors ;-)
Basically always think twice and watch your back. HR is not your friend to confide in, being disgruntled and pointing to issues need to be done carefully. In an irrational organization it will backfire -- you are labeled as a disgruntled trouble-maker.
Those engineers are usually fairly vocal about obstacles. Managers should learn to interpret this signal, suss out the root cause (usually easy) and eliminate it (usually hard).
Twitter might actually be better served by promoting some set of the folks that landed on the cut list.