This is very unusual and the broken line graphics on your board are not the same as on some other OSEPP board images I see, so I don't know what they represent. Certainly there is nothing on theOSEPP schematic indicating a difference.
It almost feels like a defective board. The ADC converter has a multiplexed input and the channel is selected among the 6 analog pins. It almost feels as if there is a defective bit in the selection register. That register is where the bits control the active channel is called ADMUX.
Run this little test sketch , and see if the selection values in ADMUX change appropriately
void setup() {
Serial.begin(9600);
//read A0 through A5
for (byte i = 14; i <= 19; i++)
{
int val = analogRead(i);
Serial.println(ADMUX, BIN);
}
}
void loop() {}
1000000 //A0
1000001 //A1
1000010 //A2
1000011 //A3
1000100 //A4
1000101 ///A5