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I am having an issue with CAMetalLayer on macOS.My app has an NSView subclass which has a CAMetalLayer. The renderer has a single command buffer per frame which has only a single renderpass for the drawable from the layer. The app update-render cycle is called by a millisecond timer on the main thread.The first issue is with MTLCommandBuffer presentDrawable. If I use this method to present, CAMetalLayer nextDrawable hangs for about a second when the app goes to the background (after this, everything goes back to normal, 60fps). This is a problem for my application, so instead I use MTLCommandBuffer addScheduledHandler and MTLDrawable present, which does not have the one second blocking problem. However, if I set maximumDrawableCount on my CAMetalDrawable to 3 (the default), nextDrawable behaves rather strangely. One frame it blocks for about 16ms (minus the app time) while every other frame it returns almost immediately. This causes an average 120fps resulting in unneccessary CPU and GPU usage. According to Metal System Trace in Instruments, these "short" frames are dropped by the compositor. I have found two ways of fixing this problem. I can set maximumDrawableCount to 2. The other, rather strange fix is to acquire the next drawable from the layer before commiting the command buffer. This however, adds an unneccessary 16ms delay before submitting work to the GPU.Using a display link callback to signal a semaphore and synchronize the main thread after presenting solves the 120 fps problem, but has another strange issue. If the frame time gets between approx. 5 and 8 milliseconds (for any reason, e.g. sleep) the compositor starts dropping frames. According to Instruments the app uses only two buffers during normal operation, while occasionally using a third when the frame time gets in the problematic range, resulting in frame drops. If it gets any higher than 8ms, the problem goes away, no frame drops and only two buffers are used.I'm seeing this on Mojave (10.14.6) on a 15" 2019 MBP, both on the integrated and the Radeon discrete GPUs. The app behaves the same on a 16" MBP running Catalina.Has anyone experienced this issue? Any thoughts? Thanks!