
USB ports aren't getting enough power. USB mice aren't power hungry enough for that, but some USB keyboards are hungry. Unfortunately, this includes clickable M models; Results range from a keyboard that won't initialize at all, to looping when trying to initialize and failing halfway, to borderline running and crashing when actively moving the mouse. Plugging a powered USB hub between the USB port on the KVM and the keyboard gets the damn thing working, but it would be much more convenient if the KVM itself had an additional external power supply.

4 Port USB 3.0 Switch Selector - Pubioh KVM Switch for Mouse, Keyboard, Printer, Scanner - 2 in 4 Out Sharing Box with Switch Button and 2 USB 3.0 A to A Cables
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🔌 HDMI 2.0 4 Port KVM Switch with 4K@60Hz, 2K@144Hz,1080P@120Hz Support, 18Gbps Bandwidth, USB 2.0 Keyboard/Mouse/Printer/Monitor/PC Selector, Audio Out/Mic In, HDR10, Dolby Vision, Dolby/DTS, HDCP2.2 Compatibility
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