The SAR Sequencer component uses an Analog Hardware Mux component inside it. The Amux Hardware sequencer has some restrictions on use. First of all AMuxHW only supports controlled analog connections to GPIOs. We have to make sure all the controlled analog connections are connected to GPIOs. In this case there is a PGA. There are restrictions in shorting multiple inputs too while using this hardware. These are the reason for the errors you are facing. One workaround to solve your issue is to use the Analog Amux + SAR ADC configuration.