I ran 50 Ultimate difficulty Magi Ring farming runs with a level 100 character.
Results:
According to Grim Tools, the drop rates should be:
Given the number of runs, I would have expected several legendary rings. Is it possible the legendary drop table is not functioning, or that its drops are being overridden by epics?
(I used DPYes Cheat Teleport, so only Orissia and Sethris spawned.)
Just bad RNG for you. 50 runs is a rather small sample size. It might drop 10 times in the next 50 runs, or 20 times in the next 150 runs.
edit: given that all the grimtools links from the magi rings db entries to the monster db are incorrect, it could be a bug indeed. See below
Very unlikely that it’s RNG rather than a bug or sth else. Getting 50 rings and an epic every time is (2/3)^50 ~ 1.5 in a billion chance.
Not sure what you are calculating there, but they didn’t get 50 rings. They got 33 epic rings in 50 runs. Which is still in the realm of possibilites, it’s just a little odd.
A, true, I looked too quickly, then it’s (2/3)^33 and turns out to be 1.5 in a million more reasonable to be just RNG
Maybe it’s related your report [GrimTools] Item Database - #747 by Volek since Grim Tools parses game files?
Legendary rings not linking to correct monster files?
That may actually be the case, the epic rings still link to the correct monster db pages.
Maybe epic rings Awaken to legendary ones? 
I went a few runs and got one just now. Maybe fault of teleport?
I actually ran more than 50 cycles before I started counting. So far, I’ve collected 33 + 37 Epic Magi Rings and 0 Legendary ones.
Is it just bad luck?
I did get Legendary Magi Rings in a previous version, but I never had this many Epic ones back then.
The current drop pattern feels clearly different from before.
That could be a reason to remove the legendary versions. But I was under the impression this was gonna be a FoA feature. Either way, this possible change shouldn’t be in the current public build. Maybe it slipped in there accidentally.
Good point. I don’t know how and when the RNG is calculated, but if you teleport directly to the monster it might circumvent some calculations that are responsible for the drop, and it defaults to the epic rings.
As shown in the other posts, there might be a bug with these items. But to be sure you should test this without teleporting to the monsters.
Yeah, I have read it.
Oh my Morgoneth…
But I got Legendary with teleporting with older version…
OK, I will try normal run 
I did 10 runs, and got 2 Legendary and 5 Epic.
Could it just be lucky, but at least there are no bug for normal playing.
Sorry for the fuss, and thank you for your information!
I just did 10 runs as well, droprate seems on point
So yeah, looks like DPyes teleport isn’t only messing with the randomization of Magi spawns, but with the loot drops too
This is weird. You could potentially teleport with in-game command line too. I wonder if it would bork the drops too.
@Sleepless Do you have any knowledge about it (Teleporting messing with item drops described in the OP)?
Mages randomizing script runs when roguelike dungeon door opens, thats fact. But default not randomized mages is the same mages, except they level calculates as charlevel*1, not script formula. But I still doen’t see any obstacles to not drop legendary rings.
The roguelike script spawns different magi for Ultimate and non-Ultimate difficulty, perhaps the map-spawned (no script run from opening door) is always the non-Ultimate variant with a different drop table?
e.g.,
records/creatures/enemies/boss&quest/eldritcharmor_roguelikemagi_01.dbr
vs.
records/creatures/enemies/boss&quest/eldritcharmor_roguelikemagi_01U.dbr
This! I checked previous version script, and now unpacked new one. Now with 1.2.1.6 ultimate mages have separate version. Need also unpack database to confirm different loottables.
Nice and handy anti-cheat feature with the door script! 
