Hello, Laskyyy!
I am a player of this mod pack. Recently, my friends and I set up a server and tried to play it online. This game is very interesting, but a serious problem has damaged our fun. We can't solve this problem, so we ask you for help. The following is a description of the problem:
The problem occurred when the client tried to connect to the server: after the loading process, we expected to show the game interface, but only saw "saving worlds" and the client crashed. The problem doesn't happen every time, but about half of them, so my friends and I could play it by trying a lot of times. I know from the log file that this is caused by an uncaught IndexOutOfBoundException, but then I can do nothing. A detailed log has been attached below.
I know it seems that you prefer to discuss everything about this module package on discord. However, to obtain a discord account, you need to use the phone number as the authentication. I have some ways to cross the GFW, but I have no way to verify the SMS code, so I have to choose Github issue through it may be not be appropriate. >_<

latest.log