I don't know the slack tolerance for the chain, but the usual fix is to replace the chain.
I recall several years ago a company (Mile Marker ??) made what was called the chain saver. It was a device that was installed and allowed the chain to be tightened up.
There were two schools of thought for the use of this thing.
One side believed that the chain saver allowed you to continue using the old chain thus extending it's life. The other thought was by extended the service life of the old chain, by adjusting the slack out, the chain would wear to the point where it would fail. Take each with a grain of salt
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