I can't execute Stop Order on Schwab with certain stocks.

Schwab is correct, Your order is being entered as a live order at 9:30 am.

 

true, it that shouldn’t matter as you need to adapt to the rules in place for the software you are using.

 

Exactly. But, why is the same order entered on a Tuesday night using Tuesday's close, not Wednesday's open?

 

Test it again to confirm.