I found sometimes the via/contact resistance is not extracted when I do parasitic RC extraction from the layout. It comes out for some kind of layout but fails to show up for others.

As far as I can guess, the contact/via resistance may be lost during the so-called network reduction. For example, if I connect one short piece of metal1 and one long piece of metal2 with a m1-m2 via, the via resistance won't be extracted if the piece of metal1 is too short. Only if both piece are long, it will be extracted.

I can give other examples if you need.
I wonder whether it's a known and resolved bug.

Thanks.

I use Diva. The typical via resistance in the technology I use is 4-8ohm. When the resistance is not extracted, I only see values like 0.7ohm in the extracted view. Those 0.7ohm are the extracted resistors for the wire segments.