So maybe I am missing something but when one of my players, a monk, adds the dagger to their inventory, it says it strikes with a d6 plus the acid instead of a d4. Other characters have it and it's a d4 plus the acid. When adding it from search it even says a d4 and d6 acid. I'm assuming it's a bug because I can't find anywhere that says a monk ups the die. 

Hi Grimmginger,

Daggers are a monk weapon. I am assuming that this Monk is between levels 5 and 10, where any attack they make with a Monk weapon can deal 1d6 damage instead of its normal damage dice. This will increase at level 11 to 1d8.

Martial Arts

At 1st level, your practice of martial arts gives you mastery of combat styles that use unarmed strikes and monk weapons, which are shortswords and any simple melee weapons that don’t have the two-handed or heavy property.

You gain the following benefits while you are unarmed or wielding only monk weapons and you aren’t wearing armor or wielding a shield:

• You can use Dexterity instead of Strength for the attack and damage rolls of your unarmed strikes and monk weapons.
• You can roll a d4 in place of the normal damage of your unarmed strike or monk weapon. This die changes as you gain monk levels, as shown in the Martial Arts column of the Monk table.
• When you use the Attack action with an unarmed strike or a monk weapon on your turn, you can make one unarmed strike as a bonus action. For example, if you take the Attack action and attack with a quarterstaff, you can also make an unarmed strike as a bonus action, assuming you haven’t already taken a bonus action this turn.

Yes, thank you, makes so much more sense. He's lvl 8, so that's it. Could not find that earlier