Just an update to this bug. It seems as though the enemies effects triggering at all (Even if no role was actually changed, ie protector to protector, fighter to fighter, and caster to caster), will disqualify you from the achievement. https://imgur.com/a/jOSXL51
This may also mean that it’s technically possible to get the achievement if the enemy roles change, so long as you can avoid their effect from triggering for your own units, but I haven’t yet tested this theory.
Update: After testing it I can confirm that enemies changing roles will disqualify you, even if absolutely nothing changed your own roles, even to themselves.