Originally hardness was not implemented; then per user request, we added the DR and resistances as an implementation of hardness, since it works in 95+% of the scenarios.
In this case, according to the information I can find. The rules seem to say that vulnerability is applied before resistance or hardness as a general principle.
https://rpg.stackexchange.com/questi...sistance-stack
The quote by the developer for that particular encounter suggests that the fire vulnerability should bypass the hardness; but that's not how the rules work in general. Unfortunately, there's no way in FG to automatically parse that information in a way to make a specific exception in this case, since the automation is written to work on the general case.
Regards,
JPG

