Why do you define an item trait as "more specific rules" than a character trait? Also, you seem to define Vulnerability and Resistance as the same rule? Otherwise "specific beats general" could never apply?

Maybe I misunderstood, but everything about this answer seems confusing to me

@Patta - General rules are things that apply across a range. Specific rules over-ride them. Example: Movement speed of a human is 30 ft. If you're a barbarian or monk, you get a specific over-ride to this, adding to your movement speed. If you take the mobile feat, you get a specific over-ride to this, adding to your movement speed. If you get Boots of Speed you get a specific over-ride to this, doubling your movement speed.

@Patta - That's a core D&D rule, specific beats general. If a rule is a general rule, like disengaging from combat prevents opportunity attacks, a specific rule such as Sentinel over-rides it and allows the opportunity attack anyways.

@Patta - that people think there's a way to be both vulnerable and resistant to an element at the same time is absolutely inane. You're one or the other. Until somebody can illustrate that you can be both vulnerable and resistant/immune to something at the same time, they're just wrong. This isn't like advantage/disadvantage where numerous factors can play in. It's very much an either/or.

@kviiri - Where is it stated that vulnerability and resistance are something you can have at the same time? It's a logical contradiction.

@LinoFrankCiaralli It's not.

That's, again, just your invention. If there was a rule that you can't have both at the same time, that rule would be in the book.

You can't make up rules and then expect us to provide explicit contradiction of them in the source material.

Also, as you see in Szega's answer, the wording of the rule accounts for the character having both by disambiguating the order in which the effects are applied.

Resistance and vulnerability are separate statuses a DnD 5e creature or character can have, and while I agree it is weird for a character to have both at the same time (and even more how the rules resolve), the question is about the rules of the game and not common sense or anything of that sort.

@LinoFrankCiaralli Even Jeremy just tells us to read the book...

For what it's worth, were I designing a DnD, I'd make resistance and vulnerability just cancel out in damage terms because that "round down to nearest even integer" is pretty much as silly as it gets...

@LinoFrankCiaralli See, this is where you lose me. Those are all different rules. Monk and other things don't say "your movement speed is 35", but instead give you a +5 to movement speed. Which is completeley different from the "general rule" that your movement speed is 30.

@LinoFrankCiaralli That's not what I asked about. I know about specific beats general, I simply don't see how it could ever apply to this situation.

@LinoFrankCiaralli Says what, where? There is evidence in the other answer to the contrary, even. Resistance is Resistance, Vulnerability is Vulnerability. They are literally completely different rules

To maybe expand a bit on my point: What makes you think that a race ability is less specific than an ability from an item? Items are not more specific than race. They simply aren't.

I think the whole specific vs general thing is a red herring here. This is all about resistance and vulnerability being mutually exclusive, and the logical contradiction @LinoFrankCiaralli asserts is caused only by the unsourced assumption that it's impossible to be resistant and vulnerable to the same damage type simultaneously. Drop the assumption, and there's no problem anymore, regardless of what is specific and what is not.