First Arduino Board Design
Perhaps it's because I'm not familiar with Kicad, but the sch and pcb symbols for the TCA9548 confuse me.  

The sch symbol has non-standard pin locations (back and forth, instead of CCW). For example, nReset should be on Pin3. 

Then on the pcb, the labels on the silk overlay don't match what I see in the datasheet for the TSSOP package.  

My point: double check the 9548 pin assignments.  

Also, I'm sure you realize that the I2C resistors are pull-ups, not pull-downs (as mentioned in your question). The web has some wonderful I2C resistor calculators (for length/speed considerations).