Problem/Bug Updating Craftbukkit from 1.19 to 1.20.1

Hey dear bukkit community,

so my girlfriend and I have this 1.19 craftbukkit server which is running fine with its Hamachi IP.
So we wanted now to explore 1.20.1, so I downloaded the 1.20.1 craftbukkit server, moved everything over (like the world) and wanted to start the server, but I always get an error stating:

Code:

Description: Exception in server tick loop

java.lang.IllegalStateException: Failed to initialize server
    at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:952)
    at net.minecraft.server.MinecraftServer.lambda$0(MinecraftServer.java:295)
    at java.base/java.lang.Thread.run(Thread.java:833)

I've already googled a bunch and found out that it has to do with the IP which I assigned to the server (my hamachi IP)
When I remove my Hamachi IP (so it's empty) the server starts perfectly fine, and I can join via localhost or my network IP.
But whenever I add any IP (my home network IP or hamachi IP) the above-mentioned crash error occurs again.

I really hope someone can help me out with this problem.
When I find a solution, I'll post it here so anyone else having this kinda problem can solve it too.

 

If I leave it empty, how should my girlfriend join the server if the server doesn't have any IP Address?

 

I've port forwarded the 25565 on my router to my local IP, but she still can't join. I also opened up my firewall ports for 25565 but also still nothing.
Isn't there any other fix to this?

 

Okay, so I got it working now. The problem was Hamachi itself (for some reason). I just had to reinstall Hamachi on my pc and now the server is starting again with my Hamachi IP as the server IP.

Thank you anyway for your kind help.