I described this issue on X: https://x.com/Nikolozi/status/1733057454978601123?s=20

I disabled calls in build 183, which should be optimising SwiftUI drawing by using Metal, but has a weird side effect in Logic for Mac where if one instance is closed other instances start dropping frame rates and UI responsiveness gets worse. I think it's related to MacCatalyst-AUv3 tech combo. At some point I will drop MacCatalyst and probably go fully native on macOS, but for now trying to come up with work arounds.

If you end up using Mela 4 beta in Logic for Mac let me know if you experience issues.