@Snaehild
I face the same problem as you.
Through my simple test, I found the problem.
This problem is raised by attacking a specific monster whose Id is 1951.
So for a workaround, you can temporarily delete the monster in your script.
Changepoints as following.
1. Comment the code in your script.
monster "pvp_n_1-5",0,0,"--ja--",1951,10,"Alon Event Warper::OnWave1";
To
// monster "pvp_n_1-5",0,0,"--ja--",1951,10,"Alon Event Warper::OnWave1";
2. Change the monster count in Wave1.
Wave1:
set .wave1,107;
end;
To
Wave1:
set .wave1,97;
end;
That's done.
This problem seems bug from rathena.
I have reported the bug to rathena.
You can track the issue https://github.com/rathena/rathena/issues/6082.
Enjoy that!