direct section 1256 contract gains and losses are not entered on form 1099-B. they get entered on form 6781. so why you got a 1099-B with trade by trade details rather than just a statement showing 1256 gain/loss is a mystery. hopefully, someone else can answer
if you received a k-1 with1256 gains and losses the net would be reported on line 11c. from there they get carried to form 6781
we can't see the k-1 or supplement so it makes it difficult to give you a complete answer
the first I have is whether the ETN produces 1256 gain/loss
(b)Section 1256 contract defined
(1)In general
For purposes of this section, the term “section 1256 contract” means—
(A)any regulated futures contract,
(B)any foreign currency contract,
(C)any nonequity option,
(D)any dealer equity option, and
(E)any dealer securities futures contract.
