Router uncooperative isn’t a huge issue since Aether is capable of working even under those circumstances by doing reverse-opens.
That situation usually happens when the router does not accept UPNP port mapping. It is possible for the router to show as ‘uncooperative’ even when the port is open — because it is a check for UPNP being functional, not a check on whether the port is open or not. You can have a non-working UPNP on your router and if you’ve manually forwarded the port, still have an open port, and Aether would not know it — it’s a P2P app, it does not have a remote server it can use to check whether your port is open or not.
In other words, if you’re seeing inbound connections, you’re good to go. You can largely ignore router uncooperative error if that is the case, it is an informational data point, not a terminal one.