So in Checkmate Trials, if You Die with Special Ammo and the Round Ends, You Keep it, but if You are Revived Mid-Round, You Lose it...
Why.
Also just in general, you are not going to see Eriana's Vow, glaives, or special sidearms in that mode at all with poor special ammo deliveries like that. You aren't one-shotting an enemy with a glaive, but you get just as much ammo as you would with a one-shot weapon. That is just poor ammo distribution.
It's no wonder it's so meta in Checkmate.
EDIT: The title of this post was updated to mention that it was Checkmate Trials specifically now that that particular Trials weekend has passed. This is just to clarify and prevent future confusion when reading this post.