Armor (chain mail), rare
You gain a +1 bonus to Armor Class while you wear this armor. You are considered trained with this armor even if you lack training with Medium or Heavy armor.
Made of interlocking metal rings, chain mail includes a layer of quilted fabric worn underneath the mail to prevent chafing and to cushion the impact of blows. The suit includes gauntlets.
Notes: Bonus: Armor Class, Proficiency: Self, Str. 13 Required, Stealth Disadvantage
this item isn't coded properly, it detracts from movement -10 speed when used on a rogue, it needs to be coded properly
This is still considered Chain Mail, and at the bottom of the description it says: Notes: Bonus: Armor Class, Proficiency: Self, Str 13 Required, Stealth Disadvantage.
My guess would be that your Rogue doesn't meet the STR requirement.
to those who replied, ty for your clarification, but this is just bad game design!
legacy(2014) elven chain: ---> doesn't reduce speed,
(2024) elven chain mail: ---> does reduce speed,

(2024) elven chain shirt: ---> doesn't reduce speed,

each are classed as medium armor, each should reduce the speed of the character, yet only the chain mail does.

but, when i set STR to 13:
what is the point of the 13 STR restriction? who's going to have 13 STR and not have medium armor prof?
- just make elven chain very rare instead of making the equivalent of a elven chain shirt and cloak of protection need to have the restriction of 1-2 ASI STR increases, jeez
re the discrepancies in 'elven chain' between the editions (2014 & 2024) I think its a legacy thing (and bad legacy descriptions). - check the italicized descriptions near the top of the page.
2014 (legacy) - https://www.dndbeyond.com/magic-items/4631-elven-chain - "Armor (chain shirt), rare"
2024 - https://www.dndbeyond.com/magic-items/9228539-elven-chain - "Armor (chain mail or chain shirt), rare "
2014 & earlier it was an 'elven chain shirt' (think Frodo in LOTR) so no speed/stealth penalties. The 'magic' was that (a) you could use it without proficiency in medium armour, and (b) +1 to AC. But the underlying mechanics of the 'chain shirt' remained the same (medium armour but no speed/stealth penalty or strength requirement due to shirt weight, etc.) In 2024 they have expanded 'elven chain' so you now have both a 'chain shirt' and 'chain mail' with the +1 and any user (can use without proficiency in medium or heavy armour respectively) benefits but with the underlying characteristics of the base 'shirt' or 'mail' hence the strength and stealth issues with 'mail'.
Item (Version) - AC - effects
Chain Shirt (2014/2024) - AC 13 - No stealth penalty or strength requirement, but, must have proficiency in medium armour
Chain Mail (2014/2024) - AC 16 - stealth penalty, requires strength 13, must have proficiency in heavy armour
Elven Chain (2014) (shirt) - AC 13 + 1; anyone can wear it (no proficiency requirement) and no stealth penalty or strength requirement
Elven Chain (2024) (shirt) - AC 13 + 1; anyone can wear it (no proficiency requirement) and no stealth penalty or strength requirement
Elven Chain (2024) (mail) - AC 16 +1; anyone can wear it (no proficiency requirement) - stealth penalty & strength 13 required
So in 2024 rogues can still use an Elven Chain Shirt, just like in 2014. But to use the 'new for 2024' Elven Chain Mail you need strength 13 and get disadvantage on stealth.
What your rogue wants for Christmas 2024 is mithral elven chain mail. No stealth penalty or strength requirement for mithral armour; https://www.dndbeyond.com/magic-items/5381-mithral-armor.
Chain Mail is heavy armor and there was no version of Elven Chain Mail in 2024