This only happens when a specific user is logged in. (ID:sdbfhsbgk)That user has the Yeti gear.
Version
47.3.0(Forge)
4.3.2508(Twilightforest)

logs
server
https://gist.github.com/yoyo0612/774ff075a6fdc2936e3b82e4f2059b78
clash
https://gist.github.com/yoyo0612/c0b9406d5d65fec4d6527a3e93440f2e

What are IceSnowball and p_21267_?