Currently as of todays date based off of Warcraft Logs there are:
11,187 Morogrim Tidewalker kills.
and of that 1,659 have kiilled vashj
in those 1,659 logs there is not a single Serpent Coil Braid. reference link Below
https://classic.warcraftlogs.com/zone/rankings/1010#boss=628&class=Mage - Not a single Vash kill with SCB logged - looking through the logs with blank trinkets in that section, none of the people benefitted from the SP increase or the 25% increase mana return (replenish mana never exceeded the 2460 tooltip maximum).
WCL’s filter feature does not show this trinket anywhere either, however items such as Warboots from Moro are also not shown, but are found individually in logs.
There is the case of loot not being given mid-raid, however, given that even top guilds in the world took more than 2-3 hours to clear, the loot would have expired for the rest of the guilds so it had to have been given out.
also looking at any single Tempest Keep log there is not a single mage with Serpent Coil Braid
this is not bad RNG. This is just bugged, out of 11,187 kills there should be braids but there are zero.