If you try catch mobs from Iron's Spells which can trade with you game crashes when mob near ritual, after you try login in world its delete mob, and lag game. After some testing its seems artifacts neck problem(1*). But if you don't have artifact neck you can catch mob normally, if you try to open trade menu in jar, game crashes(2*), after you try login in world its delete mob.
Iron's Spells Apothecarist mob in jar, if you try trade crashes game.
Iron's Spells Pyromancer mob in jar, if you try trade instantly closes trade window.
Iron's Spells Priest mob in jar, if you try trade instantly closes trade window.
Don't know its ars or Iron's Spells problem.
NeoForge: 21.1.69
ars_nouveau-1.21.0-5.1.0-all
irons_spellbooks-1.21-3.7.1
(1)crash-2024-10-16_18.03.15-server.txt
(2)crash-2024-10-17_10.45.11-server.txt

this is bug in iron's. please report the issue there.