I thought there is but apparently there is not an easy way to reach a contact form. https://boardgamearena.com/support
The suggested course of action in your case is to post a bug which you did.
The thing with bugs though, they got tackled by priority, and if you are the only one experiencing this issue, it is unlikely that something will happen, especially if the Arnak developer isn't around anymore.
I consider your problem more as a customer service thing, you should be able to play Arnak on this site, and it seems to be particularly related to your account. A community manager, which BGA does have as far as I know, should care for this. That's why I suggested to contact support, but you are right, it's not that simple. Unfortunately I cannot help you any further.
The suggested course of action in your case is to post a bug which you did.
The thing with bugs though, they got tackled by priority, and if you are the only one experiencing this issue, it is unlikely that something will happen, especially if the Arnak developer isn't around anymore.
I consider your problem more as a customer service thing, you should be able to play Arnak on this site, and it seems to be particularly related to your account. A community manager, which BGA does have as far as I know, should care for this. That's why I suggested to contact support, but you are right, it's not that simple. Unfortunately I cannot help you any further.