Need some clarification. Regarding Weapon [axe] mastery.

[CincyNeid82]

The party I play with is uses Pathbuilder for out character management. We are playing in the 2e rule set, and we all have the same player core books enabled.

The question I have is, I'm playing as a Human Acolyte Fighter, with the Unconventional Weaponry Perk, using the Dwarven War Axe, and the Axe Weapon Mastery perks.

in the rules of the Player Core book, p. 283, the rule reads as fallowed.

"Choose one creature adjacent to the initial target and within reach. If its AC is lower than your attack roll result for the critical hit, you deal damage to that creature equal to the result of the weapon damage die you rolled (including extra dice for its striking rune, if any). This amount isn't doubled, and no bonuses or other additional dice apply to this damage."

But in the Pathbuilder website the rule reads as

Choose one creature adjacent to the initial target and within reach. If its AC is lower than your attack roll result for the critical hit, you deal damage to that creature equal to the result of the weapon damage die you rolled (including extra dice for its striking rune, if any). No bonuses or other additional dice apply to this damage.

The "This amount isn't doubled" is not present in the Pathbuilder website.

our party did discover that the Fighter and the Barbarian are the only two players [that we've found] that omit from the verbiage.... Can anyone confirm which one is 100% correct, and why they would be different. Like does the Fighter and Barbarian have a feat set that allows them to double damage with Axe Mastery?

[Errenor]

Fighter and Barbarian (or any other classes) have (or don't have) nothing* (*well, unless something explicitly changes it). This text is an Axe critical specialization effect. It doesn't change with a character that uses it*.
So, Rulebook of course has preference over any Pathbuilder source. Unless there's errata which is shown in Pathbuilder, but not in the book.
But for this case this difference in rules doesn't change anything. It's just a clarification. The effect is the same:
"damage to that creature equal to the result of the weapon damage die you rolled (including extra dice for its striking rune, if any)"
Do you see anything here which allows this to double? It never allowed it, with or without clarification.
The only doubt could appear if you roll double dice for double damage instead of doubling a single roll, but this doesn't change the intention of the rule. So just select before rolling half of the dice as weapon damage dice for this effect, if you really roll like this.
Anyway, AoN has the version from the rulebook.

[Claxon]

Agreed with Errenor.

The class has nothing to do with this. The class ability is simply granting you access to critical specialization of weapons, under certain circumstances. Assuming you meet the circumstances to access the crit specialization of the weapon, it functions the same for everyone.

The axe crit specialization effect allows you to hit an adjacent target (assuming the initial roll would have been high enough too) but you don't treat it as a critical hit. And in PF2, we don't roll twice for damage on a crit, you simply double the damage rolled.

Sounds like Pathbuilder simply has a misleading error in the rules text they embedded in their website for the Axe crit specialization.

[NorrKnekten]

Not to mention that pathfinder has an explicit rule that effects you gain from a crit are never doubled from the rules regarding damage rolls.

Player Core pg. 407 2.0 wrote:

Benefits you gain specifically from a critical hit, like the extra damage die from the fatal weapon trait, aren't doubled.