Gamerules dont work

I recently made a server for me and my friends to play it. It has mods and plugins. I am OP and have permissions on all plugins and mods. i cannot make gamerules work. when i do /gamerule keepinventory true, it says gamerule keepinventory has been set to true. but when we die, our stuff is still dropped. I also tried running the command in console, it still didnt work. Also mods that add ores and mobs to the game dont work. The ores dont spawn by themselves and the mobs dont spawn either. Any way to fix this? 1.12.2 server

Okthanks keepinventory works now. many plugins and mods are still broken though. Veinminer etc

any fix for that?