I'm trying to give the cleric a holy symbol that increases a few things, their spell attack and damage rolls, and the amount healing spells heal for.

Under modifier I have Bonus -> Spell Group: Healing -> Fixed Value: 2    AND    Bonus -> Spell Attacks -> Fixed Value: 2

HOWEVER. When the cleric attunes to the item to gain the benefits. As reference, her 1st level 'Healing Word' does 1d8+7, her 'Spell Attack' # is +7, and her 'Modifier' # is +4 when not attuned.

Edit 1: This is when I only have the Bonus -> Spell Attacks -> Fixed Value: 2 active.

BUT when she attunes to this item, her 1st level 'Healing Word' NOW does 1d8+14?! Her 'Spell Attack' # is now +9 (that's what I wanted). And her 'Modifier' # is still +4. What the heck is happening?

Edit 2: When I have both of the above modifiers active. her 1st level 'Healing Word' NOW does 1d8+6? (Its gone down one?!) And 'Spell Attack' # is still +9. (Again what I wanted). How do I make this work?

The spell attack bonus is working correctly, but that’s the only one that will. The rest will have to be done manually by the player by customizing their character sheet to properly reflect those bonuses.