=Context
Friend pet collared a lightning dragon, after which chunk became a crash spot
Resolved the issue by killing entity using commands

=Assumption/s regarding cause
-My friend put the collar on a dragon part rather than the main dragon itself(?)

-Friend says enchants on collar was just herding (dont know if herding 1 or 2) maybe causing issues with modded mobs? ( modded mobs at the time involved mobs from fins&tails, creatures&beasts, and naturalist)