I just recently purchased a new 21.5-inch iMac with Retina 4K display (3.6GHz quad-core 7th-generation Intel Core i7 processor, Turbo Boost up to 4.2GHz). The mouse on this computer stutters and briefly freezes? it doesn't matter what mouse. I've used the Magic Mouse 2 that came with it. I've used older Apple mice and even a wired mouse. Any ideas why a high-end computer would be doing this? it has the latest OS.