I've built a custom Lurker of the Deep variant for my Warlock and for some reason my Grasp of the Deep equivalent ability keeps adding my Charisma to damage instead of a flat dice roll. Its supposed to be a proficient melee spell attack with no bonus damage. Any thoughts on what might be causing that? 

You set Cha for both the Action and for the modifier. Remove it from the modifier and it should work.

I must be missing something. As far as I can see I don't have an ability modifier set. Here is how it is configured:

Action Type: Spell

Ability Score Mofidier: ----- 

Level 1

Proficient: Yes

Attack Range: Melee

No saving throw data

1d8 damage

Radiant

Bonus Action

Long Rest Reset (with custom uses/Cha mod)

Not for the action, for the damage modifier. Did you set a damage modifier for the class feature? Not under “actions” but under “modifiers.”

I don't have any modifiers set. That feature only has the action and the only other modifiers attached to other features are a language and a resistance.

This is an attack, right? You make an attack roll with a d20, yes? I’m assuming that you set the relevant ability to as Cha, correct?

It seems like the Charisma ability modifier tag won't clear. This looks like it might be a system bug and not a setting. I just made a fresh test Artillerist Artificer and the force ballista also adds casting modifier damage when set to show as an attack even though that isn't included in the text.

Nevermind, its a confirmed bug. Glad to know I'm not crazy:

https://www.dndbeyond.com/forums/class-forums/artificer/55940-force-ballista-damage-bugged

Quote from CJW36 >>

It seems like the Charisma ability modifier tag won't clear. This looks like it might be a system bug and not a setting. I just made a fresh test Artillerist Artificer and the force ballista also adds casting modifier damage when set to show as an attack even though that isn't included in the text.

Nevermind, its a confirmed bug. Glad to know I'm not crazy:

https://www.dndbeyond.com/forums/class-forums/artificer/55940-force-ballista-damage-bugged

 Ahah!! Thank you for teaching me something new!!

Thanks for the assist!

I don’t think I did anything, but always happy to help when I can.