Since Minecraft 1.17, new shulkers can spawn when one shulker hits another shulker with a shulker bullet, wich can be enonomy breaker in some servers.
This Spigot plugin disables this shulker breeding mechanic. Shulkers can still spawn during new chunck generation, or by placing spawn eggs, etc.
Just put the PhoenixShulkerFix jar into your plugins folder. No further actions needed, it just works.
This plugin has no commands or permissions.
config.yml:
# Enable this, if you want to see every canceled shulker spawn attempt on the console.
debug: false