Hi, sorry to hear you had problems with this great plugin. I have been using this plugin for many years now without loosing a single beat ??
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First I had to modify the WP config file from incorrect instructions,
Can you share the wrong instructions that way the developer can investigate further.
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Next I had to change file permissions
If you had to change the file permissions then perhaps they were incorrect before the installation. What file permissions did you have setup before you had make any changes?
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Then the performance improvements were almost non-existent (recommended settings).
What plugins do you have installed? What king of server are you running? Are all your plugins and theme up to date? Are you running the latest WordPress version?
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Then after install if left a folder behind instead of cleaning up.
Can you provide more information please.
Thank you