Short version, Iron's Spells mod is having issues when Stinger Spear Shrine or Sempiternal Sanctum spawns with the Stinger Spear projectile entity.
Currently quick solution is to disable either mod. Annoying solution, datapack replace Bumblezone structure nbt files to not have the projectile in it.
See this issue report for more info: https://github.com/iron431/Irons-Spells-n-Spellbooks/issues/284
Short version, Iron's Spells mod is having issues when Stinger Spear Shrine or Sempiternal Sanctum spawns with the Stinger Spear projectile entity.
Currently quick solution is to disable either mod. Annoying solution, datapack replace Bumblezone structure nbt files to not have the projectile in it.
Hopefully will be fixed soon.