<<FeynCalc`
dm=GAD;ds=GS;mt=MT;fv=FV;

(* 1st term..... With one zero external momentum {0,λ,a}*)
g1=GluonGhostVertex[{0,λ,a},{q, λ1,a1},{-q, λ2,a2}]//Explicit;
g2=GluonGhostVertex[{p, μ,b},{ q-p, μ1,b1},{ -q, μ2,b2}]//Explicit;
g3=GluonGhostVertex[{-p, ν,c},{ q, ν1,c1},{ p-q, ν2,c2}]//Explicit
g3t=GluonGhostVertex[{-p, ν,c},{ q, ν1,c1},{ -q, ν2,c2}]//Explicit
gp=g1*g2*g3t//Contract//Explicit//Simplify
g12=GhostPropagator[q,a1,b2]//Explicit
g23=GhostPropagator[p-q,b1,c2]//Explicit;
g31=GhostPropagator[q,c1,a2]//Explicit;
gpro=g12*g23*g31//Contract;
tp= gpro*gp// Contract//FCI//Simplify//Explicit;
t=OneLoopSimplify[tp,q]//Contract;
T11=tp;
A1=OneLoop[q,t]// Contract//FCI//Simplify;
FullSimplify[A1]//Explicit;
%/.D->4

A10=A1*(4/2)
%/.D->4

(*2nd term*)
g1=GluonGhostVertex[{0,λ,a},{q, λ1,a1},{-q, λ2,a2}]//Explicit;
g2=GluonGhostVertex[{p, μ,b},{ q-p, μ1,b1},{ -q, μ2,b2}]//Explicit;
(*g3=GluonGhostVertex[{-p, ν,c},{ q, ν1,c1},{ p-q, ν2,c2}]//Explicit;*)
(*g3t=GluonGhostVertex[{-p, ν,c},{ q, ν1,c1},{ -q, ν2,c2}]//Explicit*)
g3tt=GluonGhostVertex[{-p, ν,c},{ q, ν1,c1},{ p, ν2,c2}]//Explicit;
gp=g1*g2*g3tt//Contract//Explicit//Simplify
g12=GhostPropagator[q,a1,b2]//Explicit
g23=GhostPropagator[p-q,b1,c2]//Explicit;
g31=GhostPropagator[q,c1,a2]//Explicit;
gpro=g12*g23*g31//Contract;
tp2= gpro*gp// Contract//FCI//Simplify//Explicit;
tyy=OneLoopSimplify[tp2,q]//Contract;
T11=tp;
A2=OneLoop[q,tyy]// Contract//FCI//Simplify;
FullSimplify[A2]//Explicit
%/.D->4

AA10=A1*(4/2)+A2*(3/2)//Simplify;
%/.D->4

(*cross diagram 1st term leads to T1*)

gh1=GluonGhostVertex[{0,λ,a},{q, λ1,a1},{-q, λ2,a2}]//Explicit;
gh2=GluonGhostVertex[{-p, ν,c},{ q+p, μ1,b1},{ -q, μ2,b2}]//Explicit;
gh3A=GluonGhostVertex[{p, μ,b},{ q, ν1,c1},{ -q, ν2,c2}]//Explicit;
gh=gh1*gh2*gh3A//Explicit;
gh12=GhostPropagator[q,a1,b2]//Explicit;
gh23=GhostPropagator[p+q,b1,c2]//Explicit;
(*tgh23=GhostPropagator[q,b1,a2]//Explicit
gh23-tgh23//Explicit//FullSimplify*)
gh31=GhostPropagator[q,c1,a2]//Explicit;
ghpro=gh12*gh23*gh31;
T11=gh*ghpro // Contract//FCI//Simplify//Explicit;
T=OneLoopSimplify[T11,q];
T1=OneLoop[q,T]//Contract;
B1=2*T1;
FullSimplify[B1];
%/.D->4

(*crossed diagram, second term, which leads to T, whcih differs from the correct result B2*)

gh1=GluonGhostVertex[{0,λ,a},{q, λ1,a1},{-q, λ2,a2}]//Explicit;
gh2=GluonGhostVertex[{-p, ν,c},{ q+p, μ1,b1},{ -q, μ2,b2}]//Explicit;
gh3B=GluonGhostVertex[{p, μ,b},{ q, ν1,c1},{ -p, ν2,c2}]//Explicit;
gh=gh1*gh2*gh3B//Explicit;
gh12=GhostPropagator[q,a1,b2]//Explicit;
gh23=GhostPropagator[p+q,b1,c2]//Explicit;
(*tgh23=GhostPropagator[q,b1,a2]//Explicit
gh23-tgh23//Explicit//FullSimplify*)
gh31=GhostPropagator[q,c1,a2]//Explicit;
ghpro=gh12*gh23*gh31;
T11=gh*ghpro // Contract//FCI//Simplify//Explicit;
T5=OneLoopSimplify[T11,q];
T=OneLoop[q,T5]
B2=T*(3/2)
%/.D->4

B=B1+B2//Simplify;
%/.D->4

A+B//Simplify;
%/.D->4

GluonVertex[{0,λ,a},{p, λ1,a1},{-p, λ2,a2}]//Explicit

(*  This structure of the GluonVertex with the momentum of one external line is set to zero, i.e.,   {0,λ,a} for simplicity.  *)