If you're Multiclassing and you add Spell Attack to your weapons it auto-assigns your effective stat (seemingly) based on your initial spell-casting class. As an example Cleric 1/Wizard 1 (Cleric was first) associates all cantrips with Wisdom. My Spell Attack should be +6 Firebolt from Wizard, with +2 Proficiency and +4 for 18 Int but I get +4 which is my proficiency of +2 and my Wis bonus of +2 totally +4.
Just in case I tried 'adjusting' the Spell-casting stat for Wiz to Int (as is default) but no change. I can't even add +2 to Attack because you can't adjust Spell Attack.
Also, Caster-level is extraneous in 5th ed. Character level for cantrips and Spell Slot Lvl for spells. If it's about calculating where you are on the Multiclassing table for Spell-slots yes but it needn't be listed as it's irrelevant for any other purpose.
Just in case I tried 'adjusting' the Spell-casting stat for Wiz to Int (as is default) but no change. I can't even add +2 to Attack because you can't adjust Spell Attack.
Also, Caster-level is extraneous in 5th ed. Character level for cantrips and Spell Slot Lvl for spells. If it's about calculating where you are on the Multiclassing table for Spell-slots yes but it needn't be listed as it's irrelevant for any other purpose.