you are out of space and your boards SSN have 6 bits that are the same.

only lemmons, lemonade time:

the open input of one ADC, combined with the SSN (some fancy operation.. or maybe just adding) use as seed for the random function. the project has some kind NVRAM? use the value of the first seed so the next seed will be generated using ADC, SSN and previous seed... improving the randomness, since at each iteration is more difficult two parts use the same seed.

I don't know Dallas ADC parts, nor it's resolution, but from what I observed using 8 bits AD0808 an open input presents a variable reading (1 or 2 bits - 20mV to 40mV) so I think that to be usefull you'll need a ADC with 10 or 12 bits... Is this the case?

HTH

orlando