If you create a financial incentive for a behavior, you're telling your employees you want to see that behavior. If it was a problem and KPIs work, they should have changed them to make them align more with the business needs.
And it's not just individual people modifying their behavior to game things, but more of an evolutionary process that the people who tend towards gaming things will get better bonuses, better reviews, better CVs, hence better next jobs, in perpetuity.
"Don't game it" can't be a simple solution. If there are people who game things, and they accumulate rewards for it, you will just see them out compete the nongamers. You are basically telling people to sacrifice their and their family's financial position for the sake of the corporation.
Everything can and will be gamed. But at the same time if many game it, managers will really want to see evidence of nongaming, so employees are also incentivized to signal their honesty, but this must be given some kind of channel too. If managers myopically focus on gameable metrics, then their loss. You must alwas leave a door open for receiving honesty signals through some kinds of side channels. These must always be somewhat amorphous because the moment you define them, they become gameable.
In other words, no recipe, stay alert, try to cooperate but don't be a pushover, etc.
What a cop-out. Everyone should want the company to succeed. So why not say "Hey, boss, this KPI won't work, here's what might happen..." instead of literally working less than needed to prove some point? It's dishonest.
The company has no interest in my success, why should I care if the company succeeds? It has no effect on me if it does.
"That's my only real motivation is not to be hassled, that and the fear of losing my job. But you know, Bob, that will only make someone work just hard enough not to get fired"
- Office Space
Put yourself in the same boat: if you had a team to manage, with the freedom to give them incentives, and they didn't have the effect you expected, you should be able to notice it and try something else.
That's great if the team is helpful and tells you exactly what's wrong, but you should also be able to evaluate how it's going and react accordingly, otherwise you're just asleep at the wheel.