Obviously I can't say for sure that this is a bug or not, but after over 2 weeks of Yamato, ZERO 14* weapons have dropped. I know that the drop rates are bad, but they're not worse than Deus or worse than Mother or anything.
It should be noted that this version of Yamato can drop literally any of the 14*s that were released before it as well. Lavis Cannon, Rykros Staff, EPD, etc.
Main Yamato Drops right now (drop log has 1 week of data and last week was yamato everywhere)
With these numbers, its almost impossible that yamato hasn't dropped a single 14* yet. Again, the drop rates are not high, but they're not low enough to the point of this being a realistic possibility.
In the first week of this Yamato coming out on JP, 97 total 14* weapons dropped, not accounting for triggers. In three weeks, NA has had zero 14* on rematch, 12man, and triggers combined.
First week of Yamato on JP (20 Urgent Quests of data total):
24 Cuvele Windea
22 Jupiter Tullus
7 Spread Needle
5 Cuvele Scarlet
4 Eternal Psycho Drive
3 Lavis Cannon
3 Rykros Staff
Sourced from swiki.
Even if NA has, lets say, 5% of the amount of people doing XH at that time as JP, it's unrealistic that in 2 weeks of Yamato, 0 14* have dropped especially considering the amount of 13* that has dropped in the same timeframe compared to JP. Maybe if it's also assumed that people are running less RDR on average compared to JP.
We have had 44 Yamato's, and over half of them should be accounted for in the current drop log.
This could be RNG being RNG, but at this point... I feel we have a lot of reason to believe it's just bugged.