FOSS gamedev and creative worlds

I want to set up a temporary server on my local PC for testing. I use normal Minetest, not minetest server

I set up the router to forward port 30000 to my PC and it works the first time. Connection from the internet was possible.

Then I want to add dyndns. I activated ddns support in my router and since then I get a connection timeout every time, even if I disable ddns and try to connect to the IP. I also try Exposed Host, where any connection should be forwarded to the PC. Local connections are working

I have no idea why this happens. Any idea?

Edit: I don't know why, but the server is running now