Thanks for reporting. 
This article is on the blog for a long time.
Troubleshooting Tip: “Enable drift correction”
For macOS users who also use an aggregate audio device → LINK
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I discovered this last week while trying to get a clean audio signal back into GP from my iPad. Once I enabled Drift Correction…problem gone!
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Q: Moving one slider also move one other slider. They are not in any widget group. How can that be?
A: Both sliders are assigned to the same parameter! 
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A High CPU issue. One of the culprits is a driver.
I had a CPU high usage issue with the latest ASIO on UMC204HD (Behringer) audio interface. As soon as I roll back to the older version the high CPU usage has gone. It seems the latest driver possibly causing an issue with the audio interface. I am using GP4 on Windows 10.
(source)
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The best practice: don’t combine VST and VST3 plugins in a rackspace from the same developer!
Either go all VST or all VST3.
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You can’t declare your MIDI In blocks as variables to use in a Scriptlet
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A scriptlet is essentially just another plugin, and as such is unaware of other blocks and plugins in the rackspace—just like your Delay plugin knows nothing about your Reverb plugin.
It only processes the data it receives, it can’t discriminate where that data comes from. So that’s why you can’t declare your MIDI In blocks as variables to use in a scriptlet.
If you want to do that, you’ll want to make a rackspace script (or the Global rackspace script) instead of a scriptlet.
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