Apparently, invis on a PC insta breaking charm wasn't in game until after the classic era ended.
https://everquest.allakhazam.com/his...es-2002-1.html
February 13, 2002 3:00 am
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** General **
** Spell Related **
- Charm is immediately removed from charmed NPC's when the character
that charmed them casts invisibility
Not sure how invis on a PC using charm worked preceding this, but it suggests the current instabreak is incorrect, making charm classes and items like the Goblin Gazughi Ring unclassically powerful.