I have possibly got the same unit as you mine is the 5GB usb solution, I didn’t even know about the tap CTRL CTRL 1 & 2 to switch systems and had been using the button on the front of the KVM but just tried it and it worked perfectly, my suspicion would be that either your keyboard or mouse is interfering somehow.
For reference I run a razor deathadder and a Hyper X alloy Elite RGB off the Back hid controls on the KVM, I run a hub off the front panel connector showing the USB symbol and nothing off the front hid connector.
Although I have been told that the front hid connector does work for this stuff, I found that when a device is plugged into it the computer needs to be rebooted in order to detect it and after detection it’s a 50/50 shot if you are lucky as to if it will work or not.
I tried both a mouse and an EPos 300 DAC and headphones and while both were detected after a reboot, neither would work in that slot.
Hope this helps.
Addendum, and this is oddly specific, I have my razor deathadder v2 plugged into the rear HID port, if I then plug a razor deathadder ESSENTIAL into the front hid port - that will work also but if I unplug the essential and attempt to move the V2 to that port the V2 will not work even if I power cycle the KVM.