DNS server conflict in proxmox subnet

Not too sure how your setup works as this is definitely a DIY route I have not taken myself. That said, there might be other people of the community that will commnet here if they have more knowledge on how to resolve your current issue.

That siad, you might want to look at one of the following posts here on the forum, as they might give you some insights into the opening of ports to StartOS:

Guide: Bolt cards, Lightning Address and Reverse Proxy all the things

How To - Exposing electrs and bitcoind over LAN in StartOS 0.3