A PC without ARC support and an Apple TV 4, with ARC support, are connected to a TS1G1,
The Apple TV to e.g. HDMI3 and the PC to HDMI2. The problem that occurs is a scrambled screen.
Solution
Install firmware 1.1.2/Central 4.2.1 and put the device with ARC support onto HDMI2 and other device (without ARC support) e.g. on HDMI3.
Furthermore be sure that the Apple TV is on its latest firmware.