Can you provide basic information like a image?
Unable to play Seirawan Chess 960

You should probably also post this to the Bug Reports thread in this club: https://www.chess.com/clubs/forum/view/bug-reports-10

@ChessMasterGS Were you able to replicate it on your end ?
First s-chess - edit position - copy the necessary code then go back and press 960 and add Seirawan in rules then add the code.

I want to convery that i were able to play a custom position that were 'pre-set' but not randomized by the website. It seems like the bug might be related to 960 + Seirawan somehow.

What do you mean. 960 option is greyed out from the rule section for Seirawan in the fist place.
It has to be random, not a pre-set position to make it valid.
I'm unable to play with opponent, although i can analyze.