My server is crashing cause of ticking entity

my server crashed multiple times, the first two times were caused by the "death" of a creeper so not the creeper itself, the third time were caused by when i spawned and killed a creeper in creative and changed to survial, the crash report told me it was because of a skeleton. this does not occur on single-player so it must be plugins not the mods, but here are the mods and plugins used anyways: Mods= SimplyTools, LibX, backpacked. Plugins= EssentialsX. logs: https://mclo.gs/ni1dAaK