Server is my and Liborsaf.
Problem fixed with another version minecraft_server.1.12.2.jar https://www.minecraft.net/en-us/article/minecraft-1122-released and fixed another problems + added support for plugins (on server) with https://github.com/CatServer/CatServer (Is better without custom sponge for CatServer. Unfortunately my items disappeared from inventory from mods: ussefull backpack and mystcraft, I don't know any more.)
My modpack is primary on forge 14.23.5.2838 Tested versions with crashing: 14.23.5.2837, 14.23.5.2836, 14.23.5.2835. It is problem MC vanilla server.