Players can set beacon effects they aren't supposed to, potentially even invalid ones causing server crash

Players can set any effect on a beacon not just the "intended" ones. Additionally setting an invalid effect will cause the server to crash. See validateEffect calls in https://hub.spigotmc.org/stash/projects/SPIGOT/repos/craftbukkit/browse/nms-patches/TileEntityBeacon.patch#86 to resolve this.

It may be better to fix whatever the root cause of the invalid effect crash is instead though.