Minecraft has a long-standing problem with achievements. If you have a lot of mods and players, the minecraft server will have a low tick rate due to the constant checking of all players' inventories for items to issue achievements to the player. If you have a lot of mods with huge NBT tags, this will only make the problem worse.
This mod tries to fix this problem by adding skip ticks for checking achievements. Additionally, adds optimizations to the achievements code.
Feel free to write about all problems and suggestions on my github! Good luck!