I have a character that has an item granting +2 to spell attacks and spell save DC, using the magic item Modififiers Bonus -> Spell Attacks and Bonus -> Spell Save DC, both with a fixed bonus of 2 (for +2 to each).

However I've noticed that these bonuses are not being applied to cantrips gained via the Pact of the Tome Warlock Pact Boon at 3rd level, which are using only the basic (unmodified) spell attack bonus and spell save DC.

What's strange is that this issue only appears to affect the Pact of the Tome; the character in question is a Bardlock (levels in both Bard and Warlock) yet the bonuses are correctly applied to Bard spells, Warlock spells, Magical Secrets, spells granted by magic items and so-on.

The only exceptions are the Pact of the Tome cantrips. Is it possible that the cantrip choices configured for the Pact of the Tome are in some way misconfigured? There is nothing in the rules to suggest that these should be ineligible for the bonuses.

It's an implementation issue with DDB. Spells that are granted via (sub)class features and not selected via Manage Spells don't get bonus modifiers applied correctly.

Edit: Hrm, but you say the bonus modifier does apply to the Bard Magical Secrets?

Any chance you could post the url to this character?

Edit2: Well did some checking with a Bard character. Huh. Maybe they're fixing those feature spells now and just haven't gotten to the Tomelock cantrips yet? Now I can't remember when they last didn't work...

Quote from naruhoodie >>

It's an implementation issue with DDB. Spells that are granted via (sub)class features and not selected via Manage Spells don't get bonus modifiers applied correctly.

Edit: Hrm, but you say the bonus modifier does apply to the Bard Magical Secrets?

Any chance you could post the url to this character?

I created a copy of the affected character (link no longer available); I swapped one of his Magical Secrets to Stinking Cloud to test this weird behaviour.

It seems like perhaps spells aren't affected but maybe cantrips are, as I also tried adding an amulet of the devout to a Death Cleric, since they get a free cantrip through the Reaper feat and it's exhibiting the same problem (should be +7 to attack, but isn't).

Update: Magical Secrets definitely isn't affected at all, both attack and save based cantrips taken via that feature apply the bonuses as expected. But the Death Domain's Reaper sub-class feature and Warlock's Pact of the Tome don't.

Cantrips are kept a bit differently than spells, even in Manage Spells, so it could be that they're taking care of the spells first. Unless Magical Secrets has been fixed all along and I just assumed it wasn't?

Quote from naruhoodie >>

Cantrips are kept a bit differently than spells, even in Manage Spells, so it could be that they're taking care of the spells first. Unless Magical Secrets has been fixed all along and I just assumed it wasn't?

It definitely seems like some kind of bug with the settings on certain features, as Magical Secrets is a feature we can homebrew correctly within sub-classes (e.g- by copying College of Lore as the template). Must be something different with how they've configured the Reaper feature for Death Domain, Pact of the Tome for Warlock and so-on that's causing it to not apply the bonuses?

I know you can create added spells with fixed save DCs, so it's not surprising that these aren't affected, but maybe some other setting is causing similar behaviour when it shouldn't? The bonuses are otherwise correctly calculated using the spellcasting stat and proficiency bonus though.

Spells added via Pact of the Tome not reflecting Spell Attacks/Spell Save DC Bonus Modifier

It’s a known bug. Pact of the Tome is a wonky one, pro’ly due to the fact that it’s Options within an Option (Pact Boons). That used to be a notorious sticky spot for everything at one point. Looks like PotT is the last holdout of that bug, Pro’ly ‘cause it’s a base class level thing.