I've just played a Bo1 Historic match against an Emergent Ultimatum deck, and it looks like the opponent won by not being able to draw a card when they had to. It would be normal if there was any Laboratory Maniac type effect active, but to the best of my knowledge (and I've looked through all the cards on the battlefield, the graveyards and the exiles) there was no such effect. Obviously I might have missed something (like another alternative win condition in effect) so this might actually not be a bug (I would appreciate an explanation in such case), but I don't think so.

I've attached a screenshot of the final state of the game (i.e. after the game deemed that I've lost), and what follows is the details.

1. Steps to reproduce:
   a. one player is playing the Emergent Ultimatum Historic deck (cards listed below, the ones I've seen at least)
   b. the EU player starts the loop (recur EU using e.g. Mizzix's Mastery -> find other cards that can recur other EUs -> rinse & repeat)
   c. they have some permanent with a triggered ability that gives them a mandatory card draw by triggering on some element of the loop (in this case it was my Outcast Trailblazer, cast from my deck by their Breach the Multiverse, triggering on 4+ power creatures (like Scholar of the Lost Trove) entering during the loop)
   d. their library gets empty during the loop, with several mandatory draw triggers still on the stack
   e. the draw effects start resolving, and the first draw with the library being empty should mean they lose; instead, their opponent (me in this case) lost on that trigger resolving.

2. Platform: PC

3. Actual results: the player decking themselves won the game on the mandatory draw trigger resolving while their library is empty.

4. Expected result: the player decking themselves should lose the game on the mandatory draw trigger resolving while their library is empty.

5. Relevant screenshot and log attached.

IMPORTANT: the log was apparently too big (~60MB) for the bug report system to let it through, so I had to compress it; but the system doesn't allow archive files (e.g. .zip or .7z) either, so I had to change the extension to .log as well. Please change it back to .7z to be able to extract it and access the proper text-file-form log file. (and since the game logs can actually get so big, there should be an easier way to attach them to bug reports instead of doing all these workaorunds).

1. Workaround: n/a.

List of the cards used by the deck (that I remember):
Scholar of the Lost Trove
Conspiracy Unraveler
Otherworldly Gaze
Mizzix's Mastery
Emergent Ultimatum
Alrund's Epiphany
Persist
Taigam's Scheming
Breach the Multiverse
Faithless Looting
That's most of them (except lands), the rest I assume can be extracted from the log (at least the ones that have been played).

Like I mentioned, I did my due diligence, and to the best of my knowledge it's a rules/mechanics/game engine bug. If not then I must've missed something, and I'm sorry to be bothering anybody, but I would greatly appreciate the explanation how this happened. Thank you! :)